As I look ahead to future studies I am wondering which language would be the better choice to concentrate on? If I were to pursue an advanced degree one of the languages will be a requirement but which is best for the long term?
Too many details are missing in your question for anyone to really help.
An advanced degree in theology or Biblical studies, like a PhD normally requires study in either French or German. The decision you make on which language to learn will depend greatly on the authors you wish to read/study. You will be expected to read authors in their original language, so choose carefully and with a view to what you hope to pursue as your primary thesis.
EDIT: clarified the scope of PhD degrees normally requiring French or German. Note, in some cases Italian, Spanish or Dutch are also options, but that is highly dependent on the particular program and course of studies.
To clarify my thinking, I was leaning towards theology with a cognitive in church history.
Try that again... Cognate in Church History
To clarify my thinking, I was leaning towards theology with a cognitive cognate in church history.
"Theology" is pretty vague. Can you be more specific?
What kind of theology: systematic, Biblical, a particular area of theology, what? Also, which stream of theology, or which historical era of theological development?If you wanted to study Lutheran theology, German would be the obvious choice. If you wanted to study Jean Calvin, French (and Latin) would be the obvious choice, though some German Calvinists might push you in the other direction (e.g., cf. the Heidelberg Catechism).
I would actually be surprised if you are not required to learn TWO research languages, being most likely German AND French. If given the option, I would learn German.
In my program, we had to pass both French and German exams by the end of year 2. German scholarship is probably more important, esp. for Semitics and historical issues.
Do you have a little bit of either one of them already from high school? Start picking up more of the language you already know a bit of and you'll find it becoming useful to you more quickly. Then add the other one once you've gained reading fluency in the one. It really couldn't hurt to know both of those languages in the long run. And Latin too, if you can manage it.