If you don't like the sound of a waterfall, then stay away from the Aquaclears. I find their waterfall a nice feature, as the sound of a waterfall is peaceful.
I have 2 AC110s on my 65-gallon, and being larger filters, they is a slight motor hum. I have an AC50 on my 20-gallon, and it's totally silent except for the waterfall.
If you get an AC110, yours might be completely quiet, motorwise. One never knows with them. I have found that the lids on mine are warped and don't seat properly unless I work with them for awhile. I find that a pain. That's probably not the case with all of them, however.
As for the function of filtering, Aquaclears can't be beat. They're great filters, overall.
I use the Aquaclears exclusively on my tanks. Aside from the small annoyances mentioned above, I'm very pleased with mine. When I get a third tank, I'll be using an AC on it, too.
20 gal. high: planted; 7 white cloud minnows, several RCS, 2 blue shrimp, 5 Amano shrimp, several snails; AC50, Azoo air. 65 gal: planted; 7 rosy barbs, 3 yellow glofish,, 3 zebra danios, 1 rosy red (fathead) minnow, 5 white cloud minnows, 3 dojo loaches, 6 crimson spot rainbow fish, several snails; AC110.