I've ran detroit rear / truetrack front, selectable front and rear, and now have an open front and selectable rear locker in the JK. All of these combos get the job done - I think alot of it really depends on cost and personal preference after you've lived with one or the other.
if you're going to get in there to do it, why not do it right with a complete setup?
what gearing are you running? I have a feeling you're probably on some pretty high gears in the diffs. you mention the word "crawl" and "control" - don't leave out the advantages that some deeper gears will have for you. I'd rather have some lower gearing with limited slips than tying up all my cash in an ARB. If you're going to have to setup the gears again anyway, this would be the time to score a set and git 'r done.
A set of 4.10's would be livable with 30" tires, perfect for 32" ~ 33" tires and be a big boost to your off-road abilities. something to think about as you're weighing the different options.
I really like the performance i've seen of a couple different rigs now with truetracks front and rear. they're strong, reliable, and they just plain work.