Sytrus hands down. You can do anything with 6 oscillators and FM/RM.

I was just about to say Sytrus, as well. I've been using it for years, but I'm still finding new things to do with it, like, I've finally cracked the code on how to make lush pads with this synth. Serum is also good for experimentation, if not better in some aspects.

Also, Fruity DX10 is heavily underestimated; apply some compression and lots of reverb, and you're set for a kick-ass pluck lead.