As always with these threads, it has to be said that you should pick whatever you personally are comfortable shooting. Just because X likes the Angel, Y likes the Ego and Z likes the Ion doesn't mean that you would like any of them. You've already experienced this yourself since you find yourself unhappy with your DM4. So this is definitely a case of try before you buy.
As a note, a longer barrel does not mean greater accuracy or range, at the very most you might find a longer barrel a little easier for you to aim, but really using decent paint, a matching barrel bore, a consistent air supply and a well maintained marker are far more important factors. Since you might find yourself having to go up field to win a game, or playing tighter than usual to try and save a losing game, you're generally better off with a shorter barrel, with a standard 12 to 14" being a good choice.
Oh, and personally I'd say go for an Angel. For realistic usage they shoot the same as all the other high-end markers out, all partisan chest-thumping aside. The maintenance requirement is little more than wiping it down at the end of the day and putting 2-3 drops of Lovejuice through the system every 4-5 boxes. The majority of times I've come across problem Angels, it's because of poor paint, poor air and/or the owner has messed around with the marker without knowing what they're doing: just feed it right and leave it to trained techs to look after and you'll be fine. But as I said earlier, that's just what works best for me: go try, then buy.