We use an assortment of vinyls here, 15", 20" & 24", and 30"
I would suggest using 15" & 30", that way for smaller jobs you have the 15", and larger the 30".
Or you may want to break it up differently, 30+" vinyl, and then a smaller size.
Larger for signs w/o overlaps, etc. and the smaller for smaller signs, decals, cut vinyl, etc. etc.
Just my opinion though, others have been in the game a lot longer than I have, so take my advice & opinons with a grain of salt..it has just been what's worked well for me.