I've tried many in the past and the Flipper is the best one I've ever used. It comes with acrylic blades to for the flipped side. I really like the fact that the scrubbing side is quite a bit bigger than the magnet side you can get it behind stuff easier and it is a lot better to see what the scrubber side it hitting. The blade side is slick, has a nice square edge, and I can run in right down the edge of the corner silicone without damaging the silicone. I recently bought another one in case they stopped making them LOL I have one in storage.
As with all scrapers though, it comes down to how clean and debris free you keep the in-tank side. All of them will scratch a tank if you let them build up sand or crap.