For prototyping (hand soldering), I've been using lead-free solder (Multicore 96SC) for over 10 years now for most small SMD soldering, but for all through-hole and wiring jobs, I mostly use leaded solder.
Why don't you use leaded solder for SMD? No such solder-paste anymore?
I must admit honestly that it's not really for an environmental or health reason. It's mainly because a decade ago or so, I had to renew my fine solder wire stock, and right when I needed to buy, I couldn't find what I was looking for as leaded solder. So I bought that, and I've been pleased with the results, so I kept using it. The particular wire I've been using (Multicore 96SC/ 3C 511) has the plus of containing a flux that I find less nasty than most fluxes I have found in leaded solder, actually, so that's also a reason. For small SMD work, I have no problem compared to leaded solder either.
But for anything with larger thermal mass, I still use leaded solder (for which I have ample stock too.)
And for solder paste, I've used both leaded and lead-free. Mostly depending on availability for that matter, since solder paste in small quantities (I'm talking for prototyping use here of course, not for production) is not always available as leaded, and you can't stock large quantities as they expire pretty fast.