What follows is just from a quick read on the site, do not take it as a final answer.
Don't trust their "recommended players", if you intend to do anything with mods, you can roughly cut it down by nearly half.
You seem to have access to the server ("full root access"), but they won't install any mod for you, so if it works, great, if it doesn't, you are on your own.
They seem to push an already modded version (bukkit), so it might not be as easy as it seems to put a FTB on that.
Apart from that, what I mainly see is that their offers are higher price that creeperhost ($8.99 on both, creeperhost gives more RAM and HDD), and the later also offers to install your FTB directly for you.
I know that was not exactly your question, but I find it useful to point it out when such differences appear, because in the end, you might want more for your money, right?