im have a fluval 202 on a 3' tank, and a rena xp4 with an ehiem professional II 2028 on a 6' tank..
my favourite would have to be fluval just over the eheim because you get a nice separator for the media basket and the hosing for me is much easier to clean. (if only the eheim came with a seperator!!!
) both the eheim and fluval seem to be equal in features and quality apart from that.
quality wise the rena seems to be a bit less well made than the others, and it has no manual primer (on mine you have to fill the intake tube with a cup to get it going and its really needs you to soak the filter material every time) but otherwise it works fine.
ive only had these for about a year so i couldnt say for the long run, but for general features and price would recommend fluval anyday.