How long do you want the filter/tank to run?
Fluvals have a nasty habit of breaking and leaking within 2 years, especially the x04 and x05 range (which are fundamentally the same range). Tetratec last better, but still have no patch on Eheim for proven longevity. There are a number of Eheims running past 20 years. If you don't believe the hype about Eheims, head over to the equipment section on MFK and see all the people looking at their oldest filters. Guess which brand gets the most mentions by a mile... Here's a clue: there's no "F" in the name of the manufacturer
There is a reason why everyone who is serious about keeping fish ends up with Eheims. Factor in the whole life costs and they are not so expensive.
Almost everyone who talks about how Eheims are overpriced and not worth their money is someone who has not owned them. Look at people like Lateral Line, CFC and Paul_MTS and others who have owned more than one brand of cannister and see what they say. I have had Fluval and Eheim, I wouldn't give my remaining Fluvals to my worst enemy, they are that shockingly poor. My lfs refuses to stock Fluval cannisters as selling such poor merchandise will hurt his reputation.
The Fluval FX-5 is a different filter which receives some good reviews and while it is a fair bit cheaper than the comparable Eheim filter, it is more costly to run and due to being mostly sponges is less efficient at processing biological waste (but conversely pulls mechanical a bit better)