Freehub vs freewheel in a singlespeed?
For maintenance and reliability, you can probably rank them in approximate order of the White freewheels being best at everything, then the premium singlespeed cassette hubs (King, Profile), then after that I'd put the nicer BMX freewheels, then the nicer generic-brand singlespeed cassette hubs (Novatec), then the junkier singlespeed cassette hubs, then the cheap BMX freewheels. It's all opinion based but that's my experience being around all that stuff.

Note that rate of engagement is a major distinguishing factor between the options (kind of the major one as far as a lot of riders are concerned), but it doesn't really follow the above order because there are some pretty nice freewheels in terms of construction with pretty bad ROE, and likewise there are any number of junky, gimmicky freewheels and cassette hubs with high ROE and bad durability.

Generally speaking, non-BMX singlespeed cassette hubs come in 130mm or 135mm, not the "trackier" 120mm, and won't be able to be respaced to 120mm because if it's well-designed then its flange-to-flange spacing will preclude that. There are BMX race cassette hubs that can be respaced up to 120 (from 110), and I'm under the impression that the Profile 120mm cassette hubs, which is the main off the shelf one that exists, are essentially a manufacturer-provided version of such a hack, but there's downside there that because the flange-to-flange was designed around a 110mm hub, you're sort of giving up strength for no reason if you space the hub 120.

I'm just going to flagrantly disregard SE rules here because the really good products in this category don't change much over time, and say that if you really want durability and reliability here you should take your pick between White, Profile, and King and call it good.