I have 3 of the AquaTop CF
-500UV filters, 2 Rena XP4 filters, 1 Eheim Ecco Pro 2232 (35 gallon) and a Fluval FX5.
The Rena, Eheim and the FX5 are well constructed. The Aquatop has cheap plastic parts that break. The Aquatop does do a great job of filtering for the money.
The Rena is easy to prime. You just need to do it once with a included funnel. The Aquatop is a challenge to prime. The Rena and the Eheim are the easiest to do maintenance on.
None of the other filters are in the same league as the FX5. It does the best filtering.