I run a 2217 on a 60 gal and plan on moving it to a larger tank & putting a 2215 on that 60. It works wonderfully for me. It's silent, it's a workhorse, and it can potentially last forever. It's also extremely adjustable, with TONS of space inside for whatever media setup you want. I haven't so much as backflushed my filter for 3 months, and it's working just as well as it was the day I put it on the tank. My tank is generally spotless- debris off the driftwood settles in one little spot, and everything else disappears into the filter. Heck, I've been running it for 6 months and I've never truly cleaned it, only backflushed it & rinsed the top filter pads. I don't think I've ever seen a piece of aquarium equipment I like more than the Eheim Classic series. I want to replace every HOB I have with Eheims, and money is the only thing holding me back.
That said, I run an AC50 on a 20 gallon, and I really like it, as well. It works really well, keeps the water clean, and I can't complain about it. But, it is a HOB, and there are drawbacks- water splashes, and it's not as flexible as the Eheim (not as much room or variability for media). Also, when it gets dirty, water flow slows WAY down. I've heard of a lot of people having problems with AC110 media baskets floating, but I can't imagine how, with looking at my AC50.
Honestly, they're probably fairly close to equal. The AC is a little cheaper, the canister will probably look better (two tubes instead of a bulky thing hanging off the back), and will be quieter. The canister offers a bit more flexibility in media, but doesn't move as much water.
Also, if you decide on the 2215, Kensfish.com has them for $95+shipping. Best price I've seen for them!