My TOP 3 Rack Extension synths I have are:
1) Predator: Great sound, super-versatile, lots of patches. Only minus is that it's a bit hard to create patches with it as the GUI is a bit meh.
2) Antidote: Super phat and clean sound. Great for basses. Great for phat synth-sounds. Super-cool GUI, easy to program new patches. Nice set of built in effects.
3) Europa: This is a stock, but it's still a RE. Really unique in soundwise. Great for textures and modulated sounds. Very versatile and has a nice set of effects included.
Bottom Line: I am settled with the synths and won't buy any new one. I might buy something special like Nemesis from the VST world. There's so many synths that sound the same anyway, so if someone wants me to buy their synth, it better impress me by it's sound, GUI and by it's easy to program factor too.
What are your best TOP 3 synths and why?