Internal filters are super quiet, but as others have mentioned, they take up tank space. So it's a win/lose.
In terms of
Canister filters, it depends on the brand. Some can be quite noisy (relatively). I had a Marineland canister filter (
Magniflow 160) that was loud enough to hear from across the room. IME, it really is a hit or miss, and depends on the specific canister filter you get.
The Fluval AquaClear HOB filters are somewhat quiet. You can hear the motor sound a little bit across the room, but it is very subtle. In my opinion, AquaClear's are among the best HOB filters.
Another filter I have used that turned out to be very quiet was the
Aqueon Quietflow. The only thing that gets noisy with these filters, over time, is the lid rattles from time to time. But the motor noise is virtually silent. You sacrifice efficiency with these filters, though, as they don't provide very much filtration in relation to the AquaClear's.
So, based on the filters I've personally used, I've had good luck with AquaClear's, QuietFlow's, and internal filters for reduced noise. The fish tank in my room, for example, has an AquaClear 20. Quiet enough for me to fall asleep with no problem.