Roger Cole
Member
If you're mostly interested in projection, I'd go with 645 or Super Slide. If you print or scan and print, 6x7 would be my choice.
If you are unsure, or like the freedom to choose after the fact, Mamiya RB 6x7, Hasselblad, and probably Bronica all have backs that will give you Super Slides when you want, and 6x6 or 6x7 if you prefer. Best of both worlds.
I was also going to suggest one of the 4x4cm twin lens reflex cameras, but you'd want to research 127 slide film first. I shoot occasionally with a Yashica 44, but only B&W and I order Efke film from Freestyle but I haven't checked the availability of color.
JD
You haven't bought any 127 Efke in a while, have you? Because it hasn't been offered in a while, since Efke went under and they sold out.
You can get film made by Maco and repacked to 127 in Japan and you can get color neg that is Portra cut down and repackaged in Canada. There's a thread about this that I was in recently after inheriting my mother's 127 Brownie. But I'm not aware of any slide film. You could probably reversal process the black and white.