I agree Classic. Ecco are pretty fidgety and the clips that hold the locking arm break easily. The Pro series is probably the easiest to prime but I still love my 2262s (aka 1500XL). As far as priming, the easiest way that I have worked out is with a small external pump. I have one that I use for WCs (I fill a 50g drum for WCS). An external pump,with a stretch of hose on it makes this simple. Back to priming - my system has 3 closed loops that are plumbed with PVC. I drop the pump in the tank and stick the output hose into the intake end of each closed loop. Turn the both pumps on an in less than 5 seconds the eheim will be running fine - and without any air noise.
The 2262 also has an additional port on the base that allows for flushing the canister between any media changes. Pretty simple.
I have ecco, pro, classic. Never had any problem with any filter. Nothing broke etc. Best one is 2262. But takes more time to clean. Profesional 3 xxl is good filter great power in bio but **** mechanical. This is reason whay i like classic more.