It all depends upon how much tinkering you want to do with your tone. A head will always be easier to deal with and is the way I would suggest you lean.
With separates, you can change one or the other for tweaking and you'll also have some more options in terms of how you power and/or match your cabinets.
For a rehearsal room setup, I wouldn't bother with separates.
"People don't realize it, but the bass player holds the whole thing up like Atlas." -Some wino who talked to me on the subway on my way to a gig