Roll film has the best variety, but I think sheet film has the greatest flexibility. It mostly depends on what you want to do. I think the question sort of puts the cart in front of the horse.
35mm has the slight edge as you can always use movie film! (but that is becomeing an endagered species) Probable even witthout that as some of the private label stuff is 35mm only.
for film varieties, no doubt 135 is the most used.
In print I prefer the format 3:4. Don't ask why, but most of my 35mm shots are cropped to this.
Then again, the square is also super. I use my Rolleicord a lot.
And I ofte work with a Mamiya7 - another fantastic camera/format.
help yourself and - good luck!
Peter