I have Fluval 404's and Rena Xp2's. From using both of these, I like the Rena series MUCH better. Granted my 404 is older, it just seems difficult to work with (getting the hose assembly unattached and starting it from stopped). The Rena, while manually primed, I think is much easier to work with. However, both are good filters.
The rena will ofter more setup options for the output which I like as well.
Two xp3 will work great
Just my thoughts.
Good luck
Aries