They both are great filters. I use more AC 110s, but I love my XP3. I'd put them head to head against any comparable filter and expect them to win without any reservation.
Look in the market place section. No code...its a special...they come with out a box or biomax but they are 19.99 and you can get biomax cheap. Free shipping on orders over 75$ and NANOREEF code gets you another 10% off.
I would take the XP3 easily. I Used to have ac110s and have XP3s now and have no regrets. The Rena is super easy to clean and mine are ridiculously quiet. The AC110 is still the best HOB on the market, but i just prefer canisters.