I have to say I hate my pro II. It leaks. I have replaced the gasket twice in the last 3 years and the canister itself is such a funky shape that emergency DIY repairs are almost impossible. My fluval leaked, but the way it assembles you can wrap a piece of silicone tape around it for a quick emergency repair while you find your replacement gasket- on the eheim Pro II, forget it- you either run a leaky filter or none at all while you scour the earth for local fish stores that have the parts on hand. Last time I had to drive to Jersey, so a part I could have gotten online for $5 cost me $12.95 + $10 GW bridge toll, a half tank of gas, and 3 hours of a Sunday wasted.
Also, the heater is much too small to handle a decent sized tank, so if you're going to need a second heater anyway, why bother spending the big bucks for the one in the filter?
I have friends who have had a lot of problems with leaks around the priming buttons as well (to the point the my local planted aquarium club actually put together a group order for replacement gaskets- and I think there are only 30-40 people in the club and I know they're not all running Pro IIs!). I've been lucky on that front so far. (fingers crossed)
I've had fewer problems with my classics, replacing gaskets is easier on the classic, (and I've only had to change one one time) and you can seal it up with a temporary fix in a jam, but they snap impeller shafts like they are going out of style, and the quick disconnects aren't well made-I was tilting the filter to get out some air bubbles after a water change and the barb on my intake split and peeled right off the disconnect - water everywhere! And again, media baskets do make life easier and the classics don't have them, you'll need media bags.
I have three filters made by eheim. Two out of three have had multiple catostrophic failures. I know that a lot of people rave about their eheims, but my experiences have not been positive.
