Range improves as you add more devices, it's a mesh network.
Depends on what you're looking for,
Aeotec by Aeon Labs • creators of Z-Wave products makes a lot of nice things. For basic things like a dimmer switch you actually have to pay attention to how well designed the dimmer circuit. Cooper and Leviton both make good switches and dimmers. Costs to license some lutron patents that recently expired have impacted whether devices broadcast their state or have to be polled. HomeSeer started making some switches that respond to multiple taps to you can make them do lots of different things (like UPB switches):
Lighting - HomeSeer Home Automation Systems but I'm not sure they pass the reliability requirement (I think there were some problems early on). The GE/Jasco switches are usually the cheapest, not necessarily the best.
UPB generally seems pretty popular with HAI users. What are you currently using?