If you plan on rooting either then i would base my decesion on aesthetics, screen size, feel in your hand, etc.
captivate: amoled screen is gorgeous!
1 gig humming bird processor is really quick when given the chance (froyo)
camera is much better on the captivate compared to the bravo. (this is really my wifes lone grip about the phone.
cons: gps issues. mine seems fine..fix within 30 secs and tracks to about 20 meters. but I have heard of some phones being not so good. this is a samsung/att issue and not a firmware problem.
That is really the only issue i have with the phone. in the stock rom (2.1) the bottom keys had a 1/2 second to 1 second delay from when i pressed to when the phone would actually respond.. this was extremely annoying for me..but all was fixed with the froyo leaks
IMO the captivate is a more advaced phone in terms of performance... screen, processor (1gig vs 800mhz), camera. (5mp vs 3mp)
however in terms of feel i prefer the bravo. seems a little heavier and a better build quality i also make less mistakes texting on the bravo..
As of right now theres not any dev's doing anything with the bravo. as you can easily see by this forum. ofcoarse this may change in the near future...
good luck with your decision... look at this way.. youre not getting an Iphone so youre already doing better than most