SERVERS TO RUN A MINECRAFT SERVER?

I currently run a 30+ player Minecraft server with 3 separate servers. There's the Wild survival with Factions and MCMMO, running with about 40 plugins on 4GB of RAM with around no lag. Then there's the Hub server, with only around 6 plugins and 1GB of RAM, and then about the same for the less-used Creatve PlotMe server, which just launched. They're all linked using BungeeCord. I currently host BungeeCord on my previous (not old) laptop which works just fine, and have paid hosting for the servers. I want to purchase two servers, one to run the Hub and Creative, and then the other running the Wild. BungeeCord can stay on the laptop. I plan to install Ubuntu Desktop 12.04 on both of them, and then possibly switch to Ubuntu Server 12.04 once everything is set up. What do you suggest? I do not have a huge experience with servers, but I've done some research and I'm confident that I can set one up, but some pointers will be greatly appreciated if there's any that can be given. What server's would be good for this kind of setup? Thanks!