I've only got about 15 years in the hobby. So far I've had pretty good experiences with Aquaclear, only one negative experience to report. I bought an AC70 brand new about 12 or 13 years ago for my parent's fish tank. I replaced it with a Fluval C3 recently because sometimes, it wouldn't power back on after turning it off (meaning the motor wouldn't start up or anything). This would happen regardless of whether the water level was high enough, or whether the filter reservoir was full of water or not. Now, the impeller in the AC70 motor had a broken fin that caused it to rattle a little, and I think that probably contributed to the no start issue. I could have just bought a new impeller for the motor, but I got a great deal on the C3 (brand new in shrinkwrap - it came in a package that I bought second-hand).
I've also had an AC20, AC50, and other AC70s that all ran fine with no issues at all. Currently I have two AC110s on a 45g, both running great. My only complaint is that they are not as quiet as the smaller filters (small amount of motor/impeller noise). I'm tempted to try out a Seachem Tidal 110.. maybe that will happen sooner rather than later.