Thinking about getting session or skater xl for xbox one. Is one significantly better or are they very similar?
The best answer is to get both.
Both games are similar in that they are simulation/realism driven. They're both different in their approach to that simulation. To ollie in SXL you hold down then release the right analog stick. To ollie in Session you need to do the same but also to flick your left analog stick up, similar to your feet IRL. Grinds have different inputs, so depending on how your brain works, one control scheme may be more intuitive to you. I generally prefer the inputs of Session over SXL.
SkaterXL is the more popular but it requires mods to get working well. Session is the better experience out of the box and 100% the better option for consoles due to the lack of mods on console. Session has a campaign (SXL does not), adjustable gameplay settings (SXL not without mods). SXL has more maps when modded. Not sure on map count/area between the two.
Session gets routine updates, paid DLC maps & DIY gear. But the core gameplay has largely been unchanged for a while now and the game desperately needs an animator as the movements look a bit janky/forced. SXL has a much quieter dev team and very few updates to the game, mostly in the maps you can download in-game. They've released some decent maps but nothing to write home about.
I prefer Session overall but I also don't have mods on SkaterXL, despite owning it on PC.
FWIW on Steam I've got 230 hours in Session and 65 in SXL. Your mileage will vary.