I've been on the receiving/admin end with both Jest Servers, and FPSplayers.
As 1LT Whitby said, Jest is rather expensive, but the quality of server and tech support is fantastic (especially if you're an Arma admin noob). FPSplayers is what SSG 2LT Johnston and I run the Mechanized server on, and it's done us very well. Their tech support has always done us well, and when our server was DDoS'ed, they sorted it right out.
There are several hosting companies you can go through, and unless you're running task force level stuff, it may not matter greatly. I think a lot more people use NFO/FPSplayers, so were you to have technical trouble, you may have a greater resource within the unit, to pull from.