Slumlord's post being a play on words notwithstanding, he's right. And not in a good way.
I've had about every brand known to mankind, including the vaunted Rigid. Rigid is no better than anything else. Walmart's around here sell a brand called "Hart" and have quit Shop Vac. Shop Vac's are okay. Hart is okay. Probably the best I've had has been Craftsman. I don't know if they sell them anymore as Sears stores around here are defunct. The cartridge filters will soon end up costing you as much as the vac itself if you use it much.
Basically, if you do much floor cleaning and bulky stuff, you want one with a big hole. They'll also do for more cramped spaces like auto interiors with the smaller hose attached-the one you use for a smaller vac.
Any brand will do. Get the big holed one of whatever brand you choose if you can swing it. They'll go on sale around here on Black Friday for $25 or used to, for a smallish one with a small hole. That was when Walmart's carried Shop Vac brand. They're okay with the limitations of the small hole, but be advised that, the shorter ones turn over easily. Get the cartridge filter, despite the extra expense.