I'd go with Lectrosonics or Zaxcom wireless. Can't go wrong with them. They get a bit pricey, but you get what you pay for.
The Lectro and Zaxcom stuff will run you $2500+ per channel, but it's outstanding. I won't do a gig with anything less than that. There's just too much danger (getting hits and dropouts) with anything less.
I like the Zaxcom wireless because of the built in micro-sd cards on the transmitters. If you run into any issues, you can pull the original recording. This will save you big time in critical situations...
Never been a huge fan of Sennheiser wireless, but as long as you get a high end set (as in $1500+), you'll be fine.
Anything less than $1500 or so, you won't find to be both mobile and stable at decent distances. You'll have to fork out good money for that.
Forgot to mention this:
Whatever you do, make sure to get a diversity system (receiver has two antennas). This DRASTICALLY reduces the number of dropouts, making your system more reliable. This is especially important when you have people moving around a lot. So whatever brand you decide on, make sure it's diversity (all your high end stuff is going to be diversity anyways).
Sweetwater has a mini article about diversity here.