Well guys let me be of some help. I own a Vibrant and i just got a G2 on a family plan for my wife. I've been using the G2 for a few days now and i have some things to say.
Lets start with the over all build quality. The G2 wins by a long shot. The Vibrant doesnt even stand a chance. The vibrant, while nice, is not original in the least, and i've had people mistaken it for an Iphone more than once. The plastic, while durable, makes the phone feel and look quite cheap. The G2, however, has a hardrubber and brushed aluminum exterrior. The phone is heavier, i would say 1.7x the weight of a vibrant and i LOVE that. The G2 feels like a solid phone in your hand. It doesnt have what people call the ''china doll'' feel. The Vibrant does have gorilla glass and im not sure what the G2 has but it feels of good quality, and im sure ill worry even less once i slap a screen protector on it. Where the G2 does get some negative marks at is the hinge. The first G2 i had i exchanged because the space bar, while it worked, didnt give a good click/tectile feed back for me, so it was just me being stupid. The 2nd g2, the one i have now, has a much more lose hinge, and im really wary about it. I kind of want to exchange it once more but im afraid i'll get one just as loose if not more loose. HTC and T-mobile really could have tought of a different keyboard hinge but alas, it is what it is.
Lets move on to the screen next. 4.0 to 3.7. Big friggin deal. I dont even really notice it. The only time i notice it is if i slap it RIGHT NEXT to the vibrant, and even then its not that big of a deal. Everything looks sharper on the G2 because of the screen size drop. same resolution but on a smaller size screen. The vibrant SAMOLED screen looks amazing but a bit exaggerated on the colors. The superlcd (also known as Super tft from what i read) doesnt look that washed out. Colors look more ''real'' and the blacks, for an lcd, look very good. Both screens respond very well to touch, and pinch zooming is very smooth on both. As for the screen, i'd say theyre equal. While the G2 may be .3 of an inch smaller, dont let it bother you.
Hardware. Ahh heres the meat of what most of you want. Let me first say this on the processors. Please dont judge processors by speed. For example, take a Pentium 4. I remember when those came out I had a 3.0ghz P4. If you were to take my laptops processor, an Intel Core 2 Duo clcoked at 2.13ghz and use only one of the cors at 2.13 ghz it would out perform the Pentium 4 processor despite the fact that its technically 870mhz slower. Why is this? Smaller die, consumes less power, makes less heat, and is more efficient. It also is of a newer generation which has better, faster, newer, and more instructions on how to process and move data. Hence efficiently. So the Hummingbird processor at 1ghz while 200mhz faster, gets out performed by the 2nd gen snapdragon at 800mhz due to the fact it can process, handle, and move data in a more efficient manner. Im not a computer whiz but its pretty simple. Both Phones are snappy, fast, and blow my socks off. Now i know the Vibrant is on 2.1 and the G2 is on 2.2 but im just giving my opinion. Also when the G2 gets a permanent root, and it will happen, you bet that you can overclock it to 1ghz. From what i read the G2 processor is just an underclocked 2nd gen 1ghz snapdragon. I will, however, have to give the overall edge to the G2. New school > Old school. Thats just the way it is.
Camera. The G2 and Vibrant both have amazing cameras but i will not lie. The Vibrant wins. Not by a big margin but not by a little one either. The Vibrant takes excellent photos and it has many many options. The G2 gives options aswell but the Vibrant feels more professionally done when it comes to the camera. The iso settings and options on the vibrant make the lack of a physical flash non bothersome. The g2, due to the fact it has a flash, just doesnt handle low light as well w/o the flash. The flash does do its job but anything past 10 foot its meh. It is the best cellphone led flash i've seen or used to date.
Some other stuff i'd like to comment on. The speaker phone of the Vibrant is loud and crisp, the G2 is a little quiet to my preferences and the speakerphone sounds tinny. The microphone sounds good on both but on videos for the G2 it has a bit of a ''tin can'' effect.
I live south west of chicago so HSPA+ hasnt been rolled out yet but i do get HSDPA from time to time. The fastest speed test on my Vibrant was about 1.8mb down and 750kbs up. On the G2 i got 4.2mb down and 1.2mb up. This, mind you, on standard 3g/hsdpa. So i can only imagine what the phone will be like once the actual HSPA+ hits. My vibrant does have the GPS JI6 update and it flys on the GPS but the G2 wins in the GPS department. I tested it many times and everytime I've connected to 11 out of 11 sats with an accuracy of 6.6 feet. The Vibrant i connect to 6 - 8 out of 11 sats with an accuracy of 25 feet.
I've tested some games on the G2 that i also have on the vibrant. The games include:
Angry Birds
Asphalt 5
Back Breaker Football
Crystal Light Defense
Angrybirds feels smooth and nice on both phones.
Asphalt 5 runs just the same on the G2 as it did on the Vibrant, and the Galaxy S phones were advertised using Asphalt 5 in commercials!
No difference in back breaker football either, and the same goes for CLD. The andreno may perform slower in benchmarks but mind you, benchmarks mean little when it comes to real world performance.
I am a bit sad that the gameloft website only shows two games available to the G2. Dungeon Hunter and Lets golf! It doesnt seem i can get desert combat, gangstar, nova, or the other gameloft games on the G2
YET i dont know if they plan on bringing them to the G2 but i know the phone could definately handle it. If a nexus one can, this phone can.
Overall im torn between which one i will use and the one i will give to my wife. She's currently inlove with the Vibrant and It wont be an easy sell getting her to the G2 if i decide to go that way, but im loving the G2 thus far...im just a bit put off by the hinge. I am going to T-mobile tomorrow to see what i can do.
Heres some fun reading
HTC G2 running at 1.42GHZ.
http://forum.xda-developers.com/showthread.php?p=8715771
Anyway I hope i've helped some of you!!!