Before deciding, on whatever you decide, be sure they allow WordPress, database access, PHP, and the requirements set by WordPress… and then look for other features you might want like autorespond, mailing lists, statistics, BBS, and whatever else you need. Really compare hard cuz there are a lot of great hosts, but when you get down to the very brass tacks, they may say they have X, Y, and Z but you end up paying more to get Z – the fine print.
There are also several sites out there that review hosts and permit the public to review the hosts they use. Check those out thoroughly to see what’s going on. Sometimes you only see the whines because people are more vocal when its a negative issue than positive, but that information can help you, too.
It’s like moving house, so go carefully and don’t kill your other system for at least three months. I used to say three-six weeks until my last move when I was told it would take 24-48 hours and I’d be ready to be up and moving and it took almost eight weeks, and six of those were with no online website because the old host’s time had run out. #$%@$%*!
