I don't know how much music you will buy vs how much music you will convert from your existing collection, but if your usage leans towards the latter, I would stay clear away from iPods.
My wife has to use one for work, which means she is forced to use iTunes. Up to today I don't know a soul who has been able to use that clunker of a software to transfer songs on the first or even fifth try. That, coupled with its proprietary file formats, means you will be stuck using all things Apple: you can't legally transfer files from an iPod to another MP3 player (you'd be defeating their anti-copying measures), you must use iTunes software to do the file transfer (instead of simply dragging and dropping files using your operating system) and you must buy from their store (you are locked into their pricing scheme and limited to what they have to offer - granted, which is a lot, but still).
Whenever possible, I never buy into proprietary formats because I like to leave my options open. Since there are perfectly viable alternatives to the iPod for listening to your music on the go, I'd stay well clear of the iPod. My opinion would change if I could listen to my purchased music on other portable devices or if I weren't forced to use iTunes, but knowing how Apple works, it'll be a cold day in hell if that ever happens.