There are tons of ROMs to choose from. As for issues, don't freak out if you hear people talk about a screen cracking. Extremely uncommon and unlikely. Some have weaker reception than in the past, but for the most part nobody says it drops, just not as many "bars." Other than that issues have been either user error or already addressed with an update.
Every phone has issues. Comparatively, the GS3 seems to have less, and it should only improve over time. I LOVE mine. I don't even care about what's coming out in the future anymore because I'm still enthralled with this device. That's never happened before with me and cell phones...