Depends on what you want really. Keep in mind FTB servers use an exorbitant amount of CPU and RAM if not configured properly.
I, personally, don't like buying servers made especially for Minecraft/FTB. That's not to say they aren't good, but it's usually a better deal to set up your own server if you know how.
If you don't know how, and want to learn, then check out these guides
here and
here.
Those are great guides for anyone new to setting up a server on their own.
I, personally, use hetzner.de, only because I live in Germany, but I've never had a problem with them. I even my RAID setup fail and I was back online within ~4 hours. They even took a nice little percentage off my bill because the server was down due to no fault of my own.