An interesting and complicated question.
I tend toward military and big padlocks. Sargent & Greenleaf 8065/8088/8077 combination padlocks (the inside of an 8065 is pretty amazing), Sargent & Greenleaf 826/831/833/951 (I haven’t found a 951 yet at a low enough price; and I think the 833 looks better than the split-case 833/951).
I would like a Rotalok but haven’t found one at a low enough price.
The large GFSP (General Field Service Padlock) version of the W-Lok is nice. Don’t take it apart unless you have a lot of patience trying to get it back together.
One of my favorites would be the Medeco Protector. Their 1970s/1980s brass padlocks were also attractive but nothing special mechanically.
One of the nice things about padlocks is they are easy to display (put another nail in the wall) compared with mortise, desk, safe/vault, and other locks.
If I had Donald Trump-like money I’d collect vault doors 😃: