If you get a Blacks', get the compact one. It'll have everything that you need. Even better, get a used compact one; it'll have everything that you need, and it'll be cheaper.
I have one that I used a bit first year, but not so much since. Westlaw has Black's online. Lexis has a dictionary, also. Your library probably has at least one copy of the big Black's if you need that.
So, overall, I'd say it's personal preference. If you'd rather look up things in a book than online, get the Blacks'.