I've had a 404 for almost two years now. While it's a great filter, I can't say that I would run out and buy another one.
I love my Rena Filstar's. I have the XP3 on my 74 and XP1 on a 29 gallon. Unlike the fluval, the Rena's are super easy to prime and also seem to push a lot more water though. Also the Rena is a lot easier to maintain and while I don't know the actualy specs, it looks like it is able to hold more media than the fluval. One of the biggest things is that unlike the Fluval, I've never had anything get stuck in the quick-disconect valves that would keep the valve from closeing when you removed it. (Plant matter was good for doing this)
I guess really this boils down to personal preference. Like I said, the fluval is a great filter and I don't have any big problems with it, but I do prefer the XP's. I bought both of them used off of the same guy for about the price I paid for the Fluval. They have at least three years of use that I know of, and are still going strong with nothing more than the occasional media change. (BTW- Did I mention they were easier to prime?)
And for the price, IMHO, the XP1's are great for the smaller tanks rather than HOB's.