I use a Sennheiser EW172 G3 with an EW172G2 as a backup. The G2 has pretty much become the "tour standard" but I definitely think the new one is head and shoulders beyond the old.
Positives
-Since pretty much every band has one, if your cable is shorting out or your body pack shits the bed, you are going to have a good shot of someone in another band having a compatible piece.
-Well respected brand, very durable.
-G3 Series has a built in tour which is very accurate and can help simplify your rig.
-G3 Series has automute on the receiver so when your body pack dies unexpectedly (it will) you don't have to worry about heinous interference noise.
Negatives
-The little cable that screws on as an 1/8" to the body pack is very prone to breakage. If it'd break on the 1/4" end it wouldn't be a big deal, but the screw on end is nearly impossible to find a replacement for. Thus you end up buying a couple $40 cables a year. I write this one up as "cost of ownership"
I'd say Line 6 is the other real option, they have a range from 200 bucks to 2k. I know some people using the G30 system. It allows you to use normal quarter inch cables which saves you from the one negative of the 172. However I heard quite a bit of audio degradation and loss of sustain when I heard it side by side with others. The people I know that have it love it, but I'm not sure I'd trust it for myself. At $300 bucks it is about 200 less than the Sennheiser though.
Good luck.