3 definitely plays better on PC than it used to, but 4 was fantastic out of the box so I'll always be biased towards it.
The biggest thing about 3 versus 4, aside from the map, is how the games are structured. 3 was the last game that gave any sort of shit about you finishing in the top 3 in your races and giving you an actual campaign of races, which you might appreciate more if you want a sense of progression. 4 replaces this with a GaaS-style long-support model, where races are things you check off a list once you've tried them once (there's no requirement to win anything besides the head-to-head showcase events, I think), and the real game is just running races over and over to gain XP, money and cars. There are technically end credits but there isn't really an "end" to the game like there is in previous Horizon games.
I spent over 100 hours in Horizon 4, so I'm not knocking the structure, but it is worth noting for someone wondering about 3.
The biggest thing about 3 versus 4, aside from the map, is how the games are structured. 3 was the last game that gave any sort of shit about you finishing in the top 3 in your races and giving you an actual campaign of races, which you might appreciate more if you want a sense of progression. 4 replaces this with a GaaS-style long-support model, where races are things you check off a list once you've tried them once (there's no requirement to win anything besides the head-to-head showcase events, I think), and the real game is just running races over and over to gain XP, money and cars. There are technically end credits but there isn't really an "end" to the game like there is in previous Horizon games.
I spent over 100 hours in Horizon 4, so I'm not knocking the structure, but it is worth noting for someone wondering about 3.