On a side note, I attended sunday's Walkon at Campaign and saw the difference between Ion's and Tippman's there.
The Tourney markers such as the Ion, Angel, Ego's that were there were great for short range rapid fire. They utterly ruled on the Speed ball field, and the close quarters matches they had a lot of advantages. People with Tippy's tended to keep their heads down on the Speedball field as they couldn't compete with the hail of paint coming from the Tourney markers.
The Tippman's, A5's, 95's, 98's and other Scenario/Woods markers had the advantage of range and accuracy. They couldn't keep up at short range or rate of fire but they could outshoot a tourney marker at range. Something I found out all too well on a few occasions when I got sniped by Tippy's from range
Ultimately you need to decide what you want to use it for. Do you want to play some Walk-on's and then progress on to Tournament play....then go for the Ion.
If you are intending on being a Walkon and scenario player only then the Tippmann's are a better bet for you.
Or better yet, go to the next Walkon and ask people there if you can try out their markers. Everyone's friendly and will probably be more than willing to let you have a little play and they can fill you in on the pro's and con's of their particular marker.