If I had to choose just one?

[Uncle E]

Go for it. If nothing else, it is a Wave-level beauty to behold. Plus, you can always add a Minitaur for Moog sounds, it’s cheap.

[cryophonik]

Man, this is a classic case of analysis paralysis

Oddball recommendation: the Bass Station. While not such an amazing sound on its own, it mixes really well with the Virus, sometimes better than fatter synths, plus you can use the Aphex Twin mode for strangeness.

Whenever I looked into it, it seems like a nice little synth. I also like the sound.

The BS2 is a pretty awesome little beast and much deeper than it appears on the surface. It's a very nice alternative to my Moogs. It has a great classic analog mono vibe, but can definitely go into some strange territory, has some filter selections that cover a lot of ground, including acid. The only letdown is that it's constructed almost entirely of plastic and feels sorta cheap, but that also puts it at a very nice price point.

[chk071]

Looks like they also upped the price on that one. https://www.thomann.de/de/novation_bass_station_ii.htm

Used to be 369 €.

There's really no reason for that. I highly doubt that online stores and manufacturers don't make good business these days.