Filters are generally more quiet than a sump, yes, however both are not really interchangable so it is not like you can simply forgo the filtration by having a sump unless you have a lot of live rock and live sand for natural filtration which, IMO and IME, is often the more costly route to go at least right in the beggining.
Regardless if a sump is loud or not, it brings so much more to a tank that it is well worth the noise. There are also many many tips and tricks to quieting them down and I cannot hear any water movement at all in my sump when I have both the little tops on it.
A sump IMO is also great because having one means that you wont have to put any or just a very few peices of equipment in the tank itself. My tank has the overflow system and the return pump from the sump back into the tank acts as two powerheads itself. Just took a bit of creative plumbing which was really really easy. If you would like, I can explain a bit more on how I did it.
I do not use any filters at all, just natural filtration and so that is why I know it is a bit more expensive when starting off. Costs can be reduced by using a lot more base rock, but that adds a lot of time to cure it and cycle the tank. I will be getting a canister filter after christmas though. I found one that is actually for a pond, but all of the media can be mixed and matched and it has a UV sterilizer and heater built right in so I think that will be well worth it all.
Since it is so hard to move a saltwater tank, I know a lot of people who just cut holes in the floor of their house and put all of the sump and filter downstairs. If it is an option for you, that would be by far the quietest. I however, like the calming sound of water falling, but it does make it hard to wait very long before going to the bathroom with all the water noises! :joke:
