If you have good enough hardware and inet connection, you can try hosting one yourself. Here is the how-to:
If you don’t want to host it at home or you can’t, look at renting either a slotted server or a dedicated server.
For slotted, I have good experience with ServerBlend.
For dedicated, others can share their experience. It is a good option if you want to run a server cluster or a populated server which will require more resources. With a dedicated server, you have full control but you still have to manage it yourself using the dedicated server launcher.