First off, you're bound to hear it from someone, but being a new driver, I'd encourage you to worry less about GPS and more about keeping your eyes on the road. Its hard enough for those of us who've been driving for many years to drive and follow GPS information/screens. I typically use mine for the maps. If I need directions, or to get around a traffic jam, I can look up my maps on the phone and the GPS will show my position in relation to the maps.
That said, here is my opinion:
First off, I've had 3 Captivates now and all 3 had the typical non-working GPS. The GPS on all 3 phones was fixed with custom ROMs. Some ROMs take longer to get a signal lock, but most like within 5-20 seconds. As for which will work for you, we can all offer suggestion, but evidence shows us that the quality of the hardware components in these phones vary so much that no one tell you which ROM will give you the best GPS functionality. For me, as far as instant lock on 8-10 sats, FireFly worked best.
First thing I'd do, is watch the videos by MobileTechVideos on YouTube. That's where I started. One thing MANY people overlook (but learn the hard way... I did), is to check your batch # BEFORE using ODIN (mentioned in the videos). If your phone is a batch 1010 or 1012 you do NOT want to use ODIN-1-CLICK. You'll want to use the ODIN3 (3 button fix version) found in the AIO Toolbox (search, you'll find it).
Anyway, I strongly encourage you to do your homework on the custom ROMs as far as installation/flashing goes BEFORE you start.
After that, the world of custom ROMs will be open to you. I've found that I like Andromeda & Continuum the best, both of which work GREAT on the phone itself, as well as gave me working GPS.