I'm a fan of the XP's myself. I probably would go with the XP4 myself, if it were my tank. I'm not a big fan of Fluvals, had one a long time ago and was not impressed. But never had the FX5, so don't know much on it. I've had XP's for over 8 years.
55G Filstar XP3 - 16" Fire Eel
75G Medium Planted - Filstar XP3 Low Light - Established Feb 2006