FWIW, I switched from HOB filters to an Eheim Classic canister about a year ago. I'm setting up a new 29 gallon tank now, and ultimately decided to get a small canister for it.
For me, the primary selling points were that I can completely silence the filter if I need to - for example, watching a movie or something - and that it restarts flawlessly after a power outage (depressingly common in my neighborhood).
The big downside is that you have to have somewhere to stash it, which can be a problem if you're putting a small-ish aquarium on a regular piece of furniture. I believe the canisters typically need to stay below water level (the Eheim instructions specify this, at least), which may also prove problematic if you want to just set it behind the tank or something, depending on the relative height. But if you have a dedicated tank stand or are using some kind of cabinet you can run the hoses into, you're set.
Oh, and you have to make sure you get all the valves closed at maintenance time or you can end up with the intake siphoning water out of the tank and all over the floor... you'll never guess how I know
Not a problem I ever had with a HOB.
I'm using Eheim Classic filters right now, and I have never replaced the media; it's all ceramic tubes and little balls and a couple of sponges, so I just clean it out when I'm doing a water change (every few months, when it occurs to me, but I'm probably supposed to do it more often than that...). It's probably paid for itself in all the proprietary filter cartridges I'm not buying.
Here's another recent thread on this topic that might be of interest:
http://www.aquariumadvice.com/forums/f15/canister-filters-whats-the-hype-342969.html