Thread: Favorite VCOs for ambient?
Braids and Plaits were mentioned. Also almost any wavetable voice would work. By changing the "index" in the wavetable synth you can get very nice timbral changes without doing a lot of work to get them. The same with Braids and Plaits as far as adjusting the timbre.
With an analog VCO (saw, triangle, square, etc.), you'll need a lot more modules to get any deep changes to the timbre. That can be a lot more expensive and an lot more room in your case.