I use Linden Lab SL viewer, but I dislike it because 2 big reasons:
1) Web profiles. Those suck! Like now... when I'm writing this... they dont work at all. Only white screen and error message. This happens too often. And they are very slow. They should be an alternate way to check profiles and we need old profiles back like they are in Firestorm viewer.
2) I need an option for disable all annoying group chats. In Firestorm we have that option.
Radar would be also good option for LL viewer, but its not necessary for me.
I would like use Firestorm instead LL viewer, but I have some bad graphic issues with it. And somehow I still like LL viewer anyway.