Good question. Both are fine cameras, and the Ultron is an oustanding lens.
I took hundreds of photos with a Rollei 35T and never found the lens to be inadequate, although it's slow at f/3.5. On the other hand, you can take the camera anywhere, because of its compact size.
The Vitessa might need some work, as it's roughly 50+ years old. So keep that in mind. Maybe you'll get one that's been serviced. It uses the famous Voigtlander "focus by dial," which you might or might not like. The body is quite a bit larger than the Rollei, but the lens is better.
Among compact cameras, you could also consider a folding Zeiss Ikon Contina II with Tessar (excellent camera with uncoupled rangefinder) or the folding Zeiss Ikon Contessa with Tessar, coupled rangefinder and meter.
Finally, there is the Voigtlander Vito III with the same excellent f/2.0 Ultron. It has a rangefinder but no meter. It's a folding version of the Prominent, although not nearly as heavy and a much better camera to use than the Prominent, I think.