They are one and the same... just differing translation, but as much as I enjoy the work of Underhill her translation feels very dated to me:

HERE BEGINNETH THE FIRST CHAPTER

Of four degrees of Christian men’s living; and of the course of his calling that this book was made unto.

GHOSTLY friend in God, thou shalt well understand that I find, in my boisterous beholding, four degrees and forms of Christian men’s living: and they be these, Common, Special, Singular, and Perfect. Three of these may be begun and ended in this life; and the fourth may by grace be begun here, but it shall ever last without end in the bliss of Heaven. And right as thou seest how they be set here in order each one after other; first Common, then Special, after Singular, and last Perfect, right so me thinketh that in the same order and in the same course our Lord hath of His great mercy called thee and led thee unto Him by the desire of thine heart. For first thou wottest well that when thou wert living in the common degree of Christian men’s living in company of thy worldly friends, it seemeth to me that the everlasting love of His Godhead, through the which He made thee and wrought thee when thou wert nought, and sithen bought thee with the price of His precious blood when thou wert lost in Adam, might not suffer thee to be so far from Him in form and degree of living. And therefore He kindled thy desire full graciously, and fastened by it a leash of longing, and led thee by it into a more special state and form of living, to be a servant among the special servants of His; where thou mightest learn to live more specially and more ghostly in His service than thou didst, or mightest do, in the common degree of living before. And what more?

Yet it seemeth that He would not leave thee thus lightly, for love of His heart, the which He hath evermore had unto thee since thou wert aught: but what did He? Seest thou nought how listily and how graciously He hath privily pulled thee to the third degree and manner of living, the which is called Singular? In the which solitary form and manner of living, thou mayest learn to lift up the foot of thy love; and step towards that state and degree of living that is perfect, and the last state of all.

 Evelyn Underhill, ed., A Book of Contemplation the Which Is Called the Cloud of Unknowing, in the Which a Soul Is Oned with God, Second Edition (London: John M. Watkins, 1922), 65–67.

Chapter I

The four degrees of the Christian life; and how he for whom this book was written advanced in his vocation¹⁰

Proemium

My spiritual friend in God:¹¹ I pray and beseech you to pay very close attention to the progress of your vocation and the way in which you have been called; thank God from your heart, so that through the help of his grace you may stand steadfast in the state, degree and manner of life that you have undertaken with full deliberation in spite of all the subtle attacks of your bodily and ghostly enemies,¹² and so win through to the crown of life¹³ that lasts forever, Amen.

My spiritual friend in God, you are to understand that according to our rather crude reckoning, there are four degrees and forms of the Christian life. They are: ordinary, special, singular and perfect. Three of these can be begun and ended in this life; and one may begin the fourth by grace here below, which is to last without end in the happiness of heaven. These degrees are set out here in order, successively, first ordinary then special, after that singular and finally perfect.¹⁴ It is in this same way, I think, according to this very order and progress, that our Lord has, in his great mercy, called you and led you to him by the desire of your heart.

First, then, you are well aware that once you lived in the ordinary degree of the Christian life in the world with your friends. And I believe that the everlasting love of the Godhead through which he made you and fashioned you when you were nothing, and then bought you at the price of his precious blood when, in Adam, you were lost, would not allow you to be so far away from him in the manner and state of your living.¹⁵ And so with his great grace he kindled your desire, and fastened to it a leash of longing,¹⁶ and with this led you into a more special state and degree of life, to be a servant of the special servants of his;¹⁷ where you could learn to live in his service more particularly and more spiritually than you did before or could do in the ordinary way of life. What is more, it appeared that he was not going to leave you alone so easily, because of the love in his heart which he has always had for you since you first existed. What is it that he did? Do you not see with what love and with what grace he has called you up to the third degree and manner of life, which is called singular? And in this state and manner of life of the solitary you are to learn to lift up the foot of your love,¹⁸ and step outwards towards that state and degree of life that is perfect, the last state of all.

¹⁰ In repeating the chapter headings, we are following R. M., who says: “Though the author of the book does not set out the various titles at the head of each chapter throughout the book, but only at the beginning, it seems better to me, all things considered, not only to put them all together at the beginning, but one by one at the head of each chapter.”

¹¹ Like three other works which can be attributed with certainty to our author, the Cloud itself is couched in the form of a letter to a young beginner from an older monk or spiritual father. (We have referred to the Carthusian practice in this regard in the Introduction, p. 40). However, it must also be noticed that many writers in this genre, with varying degrees of awareness, were simply perpetuating the tradition and adopting the style of the first apostolic writers, beginning with SS. Luke and Paul, on the understanding that their writings would be passed from hand to hand, and read aloud in quasi-ecclesiastical gatherings: in this case, monastic refectories or chapter halls. An outstanding example is the letter on the contemplative life by the Carthusian Guigo the Angelic, whose epistolary introduction is omitted in literally scores of extant MSS. Cf. The Ladder of Monks, p. 81; Introduction, supra, p. 78.

¹² Cf. Ephesians 6:10ff.

¹³ The reference to James 1:12 is taken up at length by the author in his letter on Discernment of Spiritual Impulses.

¹⁴ “The ordinary degree is of laypeople, the special of clerics or religious, and the singular of solitaries: that is, hermits, anchorites and especially Carthusians. Hence we may conclude that this book was written for a Carthusian, since in our day it is not customary, as it was in days gone by, to leave an approved religious order for a hermitage, but only for the Carthusians” (R.M.). Cf. Introduction, p. 15. The commentator on MS. Harleian 674 gives the example of Christ himself, who “whilst he was subject to his parents, was in the ordinary degree; whilst he was about his business, in the special; whilst fasting in the desert and praying on the mountain, in the singular; and in the transfiguration, resurrection and ascension, in the perfect”.

¹⁵ Cf. The Ladder: “When you were nothing I created you, and after you had sinned and made yourself a slave who once were free, then I redeemed you out of slavery with the price of myself. Then afterwards you hunted with the sinners of this world, and I caught you back from them, and I gave more of my grace to you than to others, because I wanted you to be my own” (ME version).

¹⁶ “A leash of longing.” This is one of the more outstanding examples of the author’s ability to drive home an essential theological point: the reconciliation of “you have not chosen me, but I have chosen you,” and human freedom, with a vivid and self-clarifying metaphor.

¹⁷ Hugo de Balma, in speaking of the steps to union, stresses the importance of reflecting on the benefits the disciple has received: first, of creation and of redemption by the Incarnation and the Passion; and secondly of the grace of the Carthusian vocation, which is not merely a call out of the world, “because he has called him (the disciple) not to the rule of the holy Benedict or Augustine … but has chosen him for that most blessed life which he himself chose when he was led into the desert. He was our forerunner, showing what it means to be a servant, by serving us”.

¹⁸ The source of this image is Augustine’s commentary on Psalm 9: “Rightly understood, the foot of the soul is love; for it moves by means of love to the place it is going” (PL 36, 124). De Balma speaks of the “plateau of unitive love towards which the mind hastens, supported by the feet of the affections”.

 James Walsh and Richard J. Payne, eds., The Cloud of Unknowing, The Classics of Western Spirituality (Mahwah, NJ: Paulist Press, 1981), 115–117.

So The Cloud of Unknowing is the one i recommend even though slightly more expensive you can see the annotations alone make  it a better choice.

-Dan