There are other things you should look for too, there are:
1. media capcity and media options (lack there of or flexibility)
2. Ease of cleaning (and putting back together after cleaning)
3. cost of replacement parts and availability
4. Size of hoses
5. gph output
6. reliability
7. cost
8. noise
I've been happy with my Rena Filstar XP3. It can take many types of media, is easy to clean and prime, and doesn't cost an arm and a leg. It is also readily available.
On my big tank though I'm going to try out a Fluval FX5. We'll see if it's all that it claims
Magnum 350's can be a pain in the *** with it's clips and O rings.
I also have an Eheim 2229, and it has high cost, isn't that easy to prime (have the extra priming aid),is noisey, and that it only has a choice of 2 filter medias, I may send it packing.
Tina