We have a Dyson multifloor that has treated us well. The shark my wife had before we met got to a point where there wasn't hardly any suction, even after cleaning all the filters multiple times.
We have a dog that sheds quite a bit and the Dyson does a great job getting it all. All of our surfaces are either wood, tile or short carpet so no info on the shag carpet. The one thing I don't like is the design of the wand. There's about a 2.5 ft section of rigid hose at the suction end and the hose can be a PITA to maneuver without tipping the vacuum over or dragging it around.
Yeah, that's probably my biggest complaint with mine (dyson ball allergy). It does well on normal floors but that section makes doing the stairs a pain in the ass.
Probably going to pick up one of their stick vacuums at some point.