Europa

Europa is just a really fun instrument. While I personally haven't done a whole of routing in the mod matrix; sound design and patch building can still be done quickly and powerfully. For any of you who are familiar with Thor, I have a very easy time thinking that one engine on Europa = at least 1.5 Thor instruments.
I will point out that there doesn't seem to be any FM, AM, sync, or ring mod routing between the oscillators (engines really). That would be a cool (and perhaps hardly necessary) feature.
It's not the punchiest synth in terms of sound, but I still really enjoy using this instrument every time I decide to work with it. I highly recommend it for the experience, and for the usability. It has beautiful presets, and creating your own is almost too easy.