What are some good gmod hosting sites in the EU?

Well it depends on how long time you think you will be hosting a server. If this is 2 - 3 month then you should find a game server host i did use Plugpayplay they are reliable, fast support and great optimized. If your planning on doing a long run community then i would say get a VPS or even better a dedicated server (My personal favorit)

You got huge ton of other features if you got a VPS. You can basically have alot of extra servers even on other games to while still paying the same amount. It might be more expensive but it will pay off in the long run.

You are very limited when a cpanel hoster got your server. Also alot of cpanel hosters wont let you have a mysql database without paying extra for it, same with a website you gotta pay for that.

With a VPS you can just make a database and a website but again it also requires the knowledge for it and it also requires some extra maintenance.