Is one better than the other? What's the difference?

Team JustForFans all the way.

Firstly, OF only accepts credit cards, whereas JustForFans also lets you pay in cryptocurrency. I come from a country where credit cards are not that common, only like one in three people has one. And when I started looking into the topic, it turned out it would be impossible for me at the moment to obtain a credit card. After lots and lots of research, I finally found out how to use a virtual (prepaid) one that OF accepted. Still, I see it as a big disadvantage.

Secondly, on JFF you can browse through a list of all models before subscribing. All you need is a free account. You can filter by gender etc. OF has no explore function, just a seach bar which only gets 'unlocked' AFTER you have subscribed to at least one account (it mustn't be a free account either). And even then, it sucks. NO filter options. I recently tried to find a guy who I only knew goes by the first name Skylar or an abbreviation thereof. Obviously, 90% of the search results were women. There was no way for me to get rid of those results. There also seem to be technical glitches. I entered the name of one guy who has a direct link to onlyfans on his twitter. The link works just fine, but his account wouldn't show up in the search results.

Honestly, I have no idea how that customer-unfriendly shithole of a site became so big.

Unfortunately, the whores seem to prefer OF. Idk if OF offers better conditions for performers, or if they all choose it because it's more well-known.