I've had the fluval 404, the rena xp3 and xp2 and a fluval fx5. Currently I'm running the fx5 and the xp2. The fluval 404s (I've gone through 2) were my least favorite. They were picky, I had trouble re-priming and both developed leaks over time despite replacing the rubber gaskets and such. They also went through several impellers. I couldn't recommend them to anyone.
The xp2 Rena has been great & rarely needs re-priming. My xp3 needs a new gasket or something and leaks and I never got around to repairing it so it's sitting in a cupboard. (That being said, it is about 6 years old so is due for a new gasket.) I never needed a new impeller with the renas, they were light and easy to take care of. Despite my experience with the leaky one, I would still buy another. Parts are pretty cheap. Also, they are extremely easy to take apart.
The fx5 is great. Really the only thing I don't like about it is how blasted heavy it is full of water and the screw deals on the top to open it are a pain. Because of this I don't do as much maintenance as I probably should on it. (Or maybe I'm just lazy.) However, it does have an extra valve on the bottom so you can use it to pump the water right out of the filter (not a feature I use because I like to vacuum the bottoms of my tank, but great idea) to a hose (not included with it) to wherever. You can close the valve to the input to make it empty itself into the tank. It will also stop for 3 minutes to dislodge air locks and restart itself. It's a great filter and so much room for whatever media you want in there. I use it for both fresh and saltwater applications. Another thing I like is the dual output on it, you can direct the flow wherever you want and might not even need a powerhead for extra flow. The input has a great big basket on it, which makes it practically impossible to clog up.
I've heard good things about the Eheim, but never had the opportunity to own one. (Doug on AA has one, maybe ask him). If I was to buy another canister though, I would go with Eheim or Rena (Rena is less costly I think) on a small tank (just from what I have heard about them) or an fx5 on a medium to large tank (40g or more).
For maintenance, I do the same thing as with a normal Aquaclear HOB; usually rinse the filter floss out with tap water weekly or bi-monthly (unless it looks like it needs replacing), change the carbon out every month (if I remember-changing it this often is not needed for a FW tank) and the sponges get rinsed with old tank water (if there are any).
With the fx5 the sponges can get pretty disgusting after a while (say 4 months running a heavily stocked 72 gallon full of cichlids) and I might rinse them all out in tap water, leaving the bio media in the middle alone. I prefer to take the whole canister and give it a rinse as well, which is why it bugs me that the fx5 is big. Really though, you could put a hose on it, open the valve, run the hose to a drain and pour water in instead of lifting it, I just never bothered because I don't clean it very often. The fx5 doesn't have to be cleaned every month either. I left it for about 3-4 months while running a FW planted. If you are going to leave it that long with no maintenance at all, don't put in the floss because it will clog up and cause the filter to barely run (not good for it).
Feel free to come on over and mess with the filters
