Five foot apart for dwarfs, you could plant 5 dwarfs in the space of a semi-full size tree. Spend five times as much as a semi-full size tree and get less fruit.
I'd guess a semi-full size tree would be much hardier in most conditions, last longer, and produce more fruit. You would get first fruit faster on a smaller tree, however.
An option would be to buy a dwarf, and a semi-full rootstock like the M111 (
apple) and use the dwarf as a source of scions. Plant the pair in the same hole. Graft a piece of the dwarf to the M111 rootstock. As they grow together you use the scion on the M111 as the support for the dwarf. The first couple years of fruit production comes from the dwarf. In time the semi-full outgrows the dwarf, but who cares, by then your getting production from the big tree.
I tried grafting this spring for the first time and had 100% success. I used a retractable safety knife out of the tool dolly and teflon plumbers tape to seal the tip. You can google grafting fruit trees and find loads of
video's to show you how.
You can buy rootstocks for $5 apiece, plus expensive shipping, but perhaps you could buy a bareroot tree and a rootstock from the same source and get the two trees for an extra $5. I'm thinking Fedco Seeds in Maine, Cummins Nursery in NY state, or Grandpa's Nursery, all
sell both.