I have (or have had)
(3) Fluval 304
(2) F 204
(1) F 303 (old, cylinder shape)
(1) F 302 (also the old cylinder shape)
(6) F 404 (more or less, a couple were for parts, not complete.)
Any filter can have problems, but hopefully I have enough that some parts would be interchangeable, so that if one broke the parts would be worth salvaging.
FORGET IT! Even filters with the same model number are NOT interchangeable. There are enough changes made to each model they ought to be numbered like computer programs!
Then I would have
(1) 304.1
(1) 304.2
(1) 304.3
(1) 204.1
(1) 204.2
and so on...
The internal baskets are interchangeable, but they do not break down! It is the parts where the clamps anchor to that have broken on several of them, and NONE of the top (motor) sections fit the bottom (box) sections, because they keep changing the clamp style. The way the hoses attach are slightly different. Some are interchangeable, some are not.
I have
(2) Filstar XP2
(4) XP3
There are problems here, too.
Where the hose from the tank lets the water into the filter, on top of the internal lid, inside the filter there does not seem to be much room. A couple of the XP3s slow down and will quit when a Malaysian Trumpet Snail cannot make the turn out of the hose and into the filter, then more debris gets stuck. I have removed as little as 1/2 teaspoon of rather fine debris, sitting on the lid where it probably fell out of the hose when I opened the filter, and the filter works fine after that.
I have one Eheim. (Smaller, Ecco of some sort).
It is very quiet (quieter than the others, but even the other filters are quiet as long as they are inside a stand). It is not a very strong filter, though. It doesn't plug up very often, but this is because it is not picking up as much debris.
For a while I had this one and a Fluval 404 on the same tank, opposite corners. The corner with the Fluval intake was clean, and the Fluval needed frequent cleaning, it was picking up a lot of the debris from the tank. The corner with the Eheim intake was dirty, I was frequently removing dead leaves from the area. The Eheim did not need cleaning; it had very little dirt in it.
Perhaps the Eheim would be a good filter for a shrimp tank: The flow is very gentle.
I have problems priming any of these. I get a strong pump and prime any of them by pumping water into the intake, then plugging in the filter when the water from the pump is coming out through the filter outlet and all the bubbling has stopped.