i'm debating too here's there main differences that i see on paper - i haven't seen eitehr in person yet.
- vivid 1620mah battery (5.1hr talk time), skyrocket 1850mah battery (7hr talk time)
- vivid has qhd 540x960 display, skyrocket has super amoled plus (480 x 800)
- both have snapdragon qualcomm apq8060 processor, vivid at 1.2ghz, skyrocket at 1.5ghz
- skyrocket has gingerbread 2.3.5, vivid has 2.3.4 (not a big deal since both will get ics)
- skyrocket will support nfc, it's just disabled until ics comes out, vivid unsure yet
so on paper, it all points to samsung. I'm kind of disappointed because i was really looking forward to the vivid/holiday. I haven't seen the displays side by side, but the htc has that going for it. I'm not sure how important/useful nfc will be yet.