UPRIGHTS do it with larger fan blades that create more air flow designed to BLOW a large volume of air (and dirt) over a short distance (into the bag).

CANISTERS do it with bigger motors, with but smaller fans designed to SUCK the air(and dirt) over a longer distance (from the nozzle, thru the wands, and hose into the bag or dirt chamber.

OK, so what's the third type?
We call them hybrids. They're technically canister types that are built to look like uprights. HUH? Let me explain. Uprights have always done a better job deep-cleaning carpeting and canisters were better at everything else(bare floors, furniture, stairs, walls, cars, you get it. That meant getting two machines to do the jobs right. But you know us, we want one thing to do everything. So pretty much, someone took a canister motor, mounted it on top of a rotating brush, connected them with a hose, and the upright/canister hybrid was born. Pretty much all the uprights you see nowadays with on-board tools are made like that.
Ok, so, which is better? As I said before, uprights have always done a better job deep-cleaning carpeting and canisters are better at everything else. Hybrids do both, but maybe not quite as well as the others. So you have to decide which suits your needs best.