Just keep in mind, they have several data plans, but the only one that includes tethering and mobile wifi is their 'Unlimited' one (5GB at 4G speed, anything over that at 2G speed).
Some of their bundle plans include Unlimited, but most don't and if you want tethering/hotspot with those you have to pay $14.99 extra (unless you want to use 3rd party tethering/wifi software that masks the data source, see the Android subreddits for that).
T-Mobile has decent off-contract plans, and in my area they've got good coverage. I think that's the direction I'm going when my Verizon contract is up (2 smartphones + 1 feature phone for the kid).
The network is AT&T and T-Mobile GSM and works with any unlocked phone.
EDIT: Here's an interesting listing of no-contract providers: http://forum.xda-developers.com/showthread.php?t=1455014
EDIT2: The main disadvantage (for me) of a pre-paid plan is that there is no roaming. Be sure to check the pre-paid coverage map.