I recently switched my 125 setup from an AC500 and XP3 with a 2028 to FX5 and the 2028.
I have pretty much the same experience as most users here. I don't like the spraybar and intake setup of the XP3, and I found that the flow rate in it slowed much quicker than my 2028. I think it has to do with the prefiltering of the ceramic noddles in the 2028 (whatever Eheim calls that stuff). I pretty much had to clean my XP3 3 times for every 2 times I cleaned my 2028. Could be because of higher initial flow rate, or it could be the way the filter media flow is designed.
Yes, it was louder than my 2028, but much quieter than my FX5.
I have since sold my AC500, but have kept my XP3. I think it's a great filter for the money, but it's in that territory of not cheap enough to be really cheap, but not high quality enough when you compare to Eheims. At full retail, it's tough to swallow the cost of Eheim, but you know what? I love it.
If I had 5 or 6 tanks in the 75 gallon range, there would be no doubt that I would be getting more XP3's, especially if they are in a fish room. However, for my measley 2 tanks, I'll stick with my Eheim and FX5 (and a Fluval 204 which I eventually hope to replace with an Eheim classic.