So as stated above XP is same on all. Here is another way you can view servers:
Casual: You can do whatever you want, stunts, over speed, troll, crash for fun, whatever you’d like.
Training: ATC is added in (untrained and May mis pattern you, but it’s “training”), you can get violations for going over 250 under 10,000. You can not get violations for speeding on taxiway, unless you’re over 250 kts. People can troll without punishment, they’ll just be shamed upon.
Pilots are advised to listen to atc, sometimes they don’t, but that’s people being people.
Expert: a huge step up from training server, I advise you go watch some videos and or practice atc understanding. This is based on real life, just with configurations in place. ( 100% you’ll get consistent atc ).