Atmospheres. It has come to my attention that different servers have different atmospheres. But as I've only been on 2 servers I'm going to guess those two, and I'll have a go at one other. Okay so let's go.
Cupcake Valley. Well this server is my home server and I do love it. Cupcake valley has about 2 really active big clubs and 3 kind of active clubs that are big going at the same time. Often on Cupcake Valley people will pair up with someone who they call a bae, this happens on other servers but I think it is biggest (and taken most seriously) on Cupcake Valley. CV has a small number of youtubers with between 200 and 1000 subscribers. So there is a bit of "I love your videos" going around, but not much. Sadly, there are a lot of drama llamas on CV and thus global can be hell sometimes! We do have a few lag cheaters, but I know the problem is worse on other servers.
Air Star. As the first server ever created, this Swedish server is home to some very famous players. I've noticed that editing is a big thing over there. This server probably has the most players who've been playing since the beginning of the game. Thus there will be many level 19s. Also there are about 8 really active clubs and many kind of active clubs. Very different to Cupcake Valley. There is still a bit of drama over there, but baes aren't as big. If you're lucky you might spot Michell Gladeson, Esmay Silverforce, Alicia Starnight, Ylva Moonwright, Kim & Emily, Dextra and who knows who else wondering the realms of AS!
Unicorn Forest. This server is home to the most low levels and non Star Riders (well if you compare it to CV). It is a quiet little server and has about 2 clubs that are big and active with 1 or 2 smaller active ones. If you like high scoring/ racing, this is an easy server to get high scores on, yet it has been filling up in the current months. The filter here is very annoying and hard to work with and the club names are very odd, but it is a nice server for someone who wants less of the social side of sso.