Which lead-free solder is recommended?

[jeffspc88mx]

I'm sticking with Tim's 67/33 solder suggestion (containing lead) for now, but as he points out, "lead-free isn't going away" and we might as well get used to using it. So...

is there a preferred type of lead-free solder? Which one?

Come to think of it, I have another question(s):

Why would someone NOT want to use the 67/33 solder? Is there some performance difference between it and the other alloys? And is lead-free only used for environmental reasons? Or does it have performance advantages as well?