as above really , i personally run both and thought that my fx5 had the edge slightly on my eheim canisters (ease of maintanence) until one of my fx5s top covers broken , for some reason fluval have got major problems with there plastics being brittle over time , i have replaced that filter with a pro3 and allough more expensive is in my opinion far better than the fluvals , i also have a couple of eheim canisters 2217s that are approx 15 years old now and still running ( have had to change a couple of seals and one or two impellers but thats it ).
i really wish fluval would sort this plastic issue out ,as i beleive that there filters are priced reasonably for a aquarium filter , eheim you allways feel your paying over the top (except some of the classic series) but when you consider how long the eheims last the sensible money would have to go to them