There are plenty of game modes to play in Minecraft and for every way to play there's whole boatloads of servers to play on. Finding out the right game mode is just the start of finding the server you're going to want to play for a long time and enjoy yourself on. After figuring out your game mode, you're going to want to shop around a bit to find a server that offers you the experience you want. To start with I'll go over the major game modes among the Minecraft servers.
These servers are the ones I enjoy quite a bit. There's always something going on if there's at least some people on it, the rules don't really matter since as the name suggests rules aren't really in the cards for Minecraft anarchy servers. As I suggested though you're going to want to find yourself a server that has a high enough, since when the population is low enough they feel like wastelands with no one to quarrel over, except the occasional player who spots you at a distance and simply goes the other way.
Minecraft prison servers are good because they give Minecraft the structure that it lacks in it's original form. It gives you a clear goal to work towards and makes you pretty much compete with others to achieve it. A fun game mode nonetheless as you're quite likely to wear yourself out if you don't play with friends. To find the right Minecraft prison server for yourself, shop around till you find the one that has the events and rates that seem fun to you.
While this doesn't really apply only to Skyblock challenges but to most Minecraft servers that don't really have a continuous game modes as much, like the Skyblock, the survival battle royales etc. … You want to pretty much pay attention to two things, you want the community built around those servers to be one you're going to want to engage with for a long time and you're going to want to pay attention to their events and weekly tournaments.
Basically these are some of the more popular game modes you're going to find on among Minecraft servers. There are plenty of Minecraft server lists out there and I'm sure you can take a little gander to find a server just right for you. I can advise you to use this Minecraft servers as this is the one I use.