They're all top-tier bikes and all recommended, but all different too. Cleary puts kids in a very aggressive position, which is neither good or bad. Prevelo has a very upright position, and Frog somewhere in between. Pello Revo uses a coaster brake, which I don't think is great for beginning riders, but that could come down to a personal preference. Unless you have specific requirements, any of these bikes would work. And just remember that they'll outgrow it in a year or two anyway, at which point you can re-assess based on their riding progress.