Since I'm always busy building and stuff, Imprudence is the right choice for me.
I have an older machine and the other 3rd party viewers, for me, are taking way too much PC resources. I don't have a very good graphic card and that really makes my PC go bunker at times ... lol
Also, they are programmed for SL. So when you search, you end up having the SL stuff. Some of them you cannot Import or Export.
As for the Zen viewer, I have a heck of a time logging in with that one. Unless I go to one of the plazas, it won't let me log in. Then, once I do finally managed to log in at one of the plazas, most times I can't TP to any other regions. Again, it's probably because of my older machine.
But when I take a break from building and want to go snoop around the other regions, I log in with Phoenix to make sure I don't miss out on the wonderful mesh stuff out there. So I'm with Sarah on this one. Those of you talented enough or brave enough to handle mesh, please keep at it.