All those camera shop branded ones are utter toys. So is all that Amazon crap. But admittedly, most folks aren't wiling to pay for anything of serious machinist quality, but that's the kind of source where you'd look. A decent torpedo level has a strong casting and a machined prime edge. Stabila is a good brand at reasonable price, well below machinist pricing. Stanley and other home center brands usually aren't reliable enough for the scarecrow of the Wizard of Oz. I've seen em all sectioned in half in order to sort marketing BS from fact. Quite a bit goes into a good level, even a tiny one. Or for an assortment of basic options, go to the appropriate page of the McMaster online catalog. If you need cheap, a gravity pendulum angle finder will be way more accurate than any inexpensive level. I always kept one of those in my architectural shooting kit.

Any serious small twin-vial level like the Starrett cross-test bubble level is designed to be so precise that you'd go nuts trying to level it on any camera or tripod surface anyway. A simple single-tube Starrett pocket level is more realistic, and won't cost you a hundred bucks. If you want a little acrylic cube level, I again recommend Stabila, but won't go into the "why" of it here. Let's just say that for every level you've ever seen, I've probably sold a thousand professional ones, and know the fine details of manufacturing which make a real difference.

But unless your purpose is for sake of stitching exposures, any architectural nitpickiness falls apart due to the fact that film seldom sits precisely square in the holder itself, and buildings are seldom truly level and plumb. True squaring should be done during the printing step. The newest, tallest, and most expensive highrise building in SF is fully 18 inches out of plumb top to bottom, and the error can be seen with the naked eye, especially in relation to adjacent tall buildings. No camera level can cure that; even the engineers are having a hard time figuring out how to correct it. But lawyers are sure having a happy field day over it.