G2:
800mhz proceesor
3G+ but 14.4 mbps is the cap due to processor
3.7inch TFT LCD display (16-bit)
8gb micro included expandable to 32gb
2.2 android out of the box
Physical keypad
5mp camera with flash

Vibrant:
1ghz processor
3G (max around 7-8mbps)
4inch AMOLED display (24-bit)
2.1 android out of box (2.2 unknown)
5mp camera, no flash but has amazing night mode

Both are very comparable. Hard to choose especially since they are the same price either in or out of contract.

IMO they both have pros and cons, and it is not enough to rip them apart.

You really need to look at them closely at the store, and get a rep that is not bias.

I have the Vibrant, love the phone! G2 is a contender, but i am not dropping my Vibrant for it. And if i had the G2 first, I am pretty sure I wouldn't have dropped it for the Vibrant.

These are two phone that you cannot go wrong either way.