the 2227 is the wet/dry version, with a self priming unit and fairly sophisticated technology,
the 2236 ecco isn't in the same league as the other two and is a cheap version IMO and i'm sure isn't even made by eheim
the 2217 is self priming and has only one running part but is known to last for around 20 years if maintained properly, It also has a higher flowrate than the other two filters,
At the end of the day it really comes down to the priming aspect IMO, if you want an easy life then go for the self priming 2227 but if you don't mind spending a little time syphoning water into the cannister to start the flow on startup then the classic 2217 is well worth it at half the price of the 2227