HTC HD2 is much much better than Vibrant.If you want paralized camera without flash you can go for Vibrant,If you want UI that often neglected by reviewers then you can go for Vibrant,If you want sensitive plastic phone then you can go for Vibrant.
For HD2 here goes your list;
If you want to try everything best that you can do with a phone then HD2 is for you.
HD2's own UI is attractive but you can install Sense 3.0 on it which is the best.
HD2's camera has Dual LED Flash,your photos wont look nightmare as they do on Vibrant at night.(and super amoled has nothing to do with it).
HD2's solid build quality ensures that you have something high quality at your palm.
HD2 could be dual booted which means you can run 2 OS at the same time.(No Windows or Android phone can do that).
HD2 has physical buttons which many people prefer instead of capacitive ones.
HD2 has more RAM than Vibrant (576 vs 512) so that means HD2 is physically 15% more responsive and better for multi-tasking.
HD2 has much better resale than Vibrant all across Pakistan.
If you have a believe on crap benchmark ratings then HD2 explodes in Benchmarks too if you put Android on it.
You can even run Ubuntu,Windows 7,Windows XP,Meego,Maemo,Android on HD2 and what's more.?
You can also learn SD Card ROM Hacking method on HD2 which protects your phone if something bad happens.
PRICE FOR HD2 would be around 25-29k used and 34-37k brand new depend up on SADDAR and CHEN ONE KHI
Moreover its on you.Thank you.