I have several eheims, classic and pro series, and a fluval 304. Fluvals are easier (for your lfs) to get parts for, but you can find just about anything for eheims online. The catch is, you need to buy parts for the fluvals more often than for eheims. The classic series (2215) in particular are very well-designed for long-term durability. The main difference between the two in terms of performance is the flow rate. If you're stocking a tank with cichlids and pleco's and you want more flow to keep the tank clean, go with the FX5.
A planted tank stocked with smaller, less messy fish is another matter. The eheims are rated for tank size/capacity for biological filtration, not mechanical. I use a 2215 along with an air-driven hydrosponge filter in a 40 gallon tank. It housed several hundred endlers and a tank full of Najas last year. I picked up a Carapo knife to thin out their numbers, and when there were less than 2 dozen remaining the survivors were moved to another tank. I then tossed in dozens of extra cichlid fry, which didn't get eaten as quickly, so now there are several dozen ~3" fish along with the Carapo in the tank. The Najas has been eaten by the cichlids, but the eheim and hydrosponge still support the bioload and keep the tank looking clean.