RAM makes a great point. VHF can pick up so many different things, from radio transmitters, to walkie-talkies, to all sorts of other goodies. I used to have several VHF lapel mics, from a crappy $50 Tandy (Radio Shack) to something similar to the PRO series from Azden.
The sound quality is lower on VHF, plus it has much larger "dead zones" indoors. Because the band is wider, VHF mics can have 3 foot wide dead spots, wheras UHF is usually 6 inches to a foot wide. Taking that to Wedding videos, The VHF mics can lose signal in an area as big as the area the pastor, bride, and groom are stading in on stage, where a good UHF might only lose signal for a second if the pastor shifts his position during the ceremony.
Of course, UHF isn't a miracle child, either. The upper bands of Uhf (900's+) are used by stuff like garage door openers, cordless phones, wireless transmitters, etc... which can give you a lot of noise.
Your best bet is to aim for a mid-range UHF setup. I have Azdens 200ULT package that comes with two mics. The other nice thing is that you can't accidentally switch frequencies on these mich, unlike their VHF counterparts with the frequency switch right on top, in line with the power switch.
Ultimately, it's up to yu though. Either mic will work beautifully under ideal circumstances, and each mic has issues tht make some circumstances less than ideal. But if you have the budget, I'd go with UHF