I have a Fluval, Rena, and Cascade.
The Rena Filstar is nice but hard to prime. I like everything else about it, especially the quick release valve for the hoses.
The Fluval is nice, with the quick release valve and they prime better than the Rena.
The Cascade is great, with a wonderful prime, but no quick release for the hoses. You have to turn the valve and unscrew the hoses rather than just pull one lever. Cascade isn't even listed on their sale.
Eheim used to be terrible to prime, but the Pro 2 looks like a similar priming mechanism as the cascade.
I am not a fan of Marineland products.
There are a ton on there I've never heard of that sound neat, like the Aquael. Google and check reviews on the specific canisters.