Matt: I've only ever used the Mag-floats, so I can't really comment on what is the 'best'. However, I did want to caution you that whatever you get, I don't believe any will be "scratch-proof". You have to be REALLY careful when using them, since anything that gets between the cleaner & the acrylic could cause damage. Some common problems I've run into is sand & little tiny baby snails. I'll be cleaning away & not realize I got a little grain of sand or baby snail stuck between...then next thing I know I've got a new long scratch.
I still use the magnet cleaner, but only when I'm feeling lazy. Otherwise, I do it the old fashion way of sticking my hands into the tank & using a scrub pad. I end up paying much closer attention that way vs using the magnet cleaner.
I did nothing but scratch my acrylic tank with an "Acrylic Algae Magnet" . I personally would never use a magnet on acrylic, especially one as strong as a magnavore (which I have on my glass tank). JMO.