I can't say for certain as I know these keyboards only from a distance. But from conversations I tend to think that Korg PA arrangers are the most adjustable when it comes to editing. I think it worth to have a look at manual (reference manual) of a specific keyboard to get an idea. Some people say that synth sounds is where Korg is better, and Yamaha is better at acoustic sounds. As for Roland EA7, well, personally I'm not convinced that it sounds advanced enough for its price, but there are those who like this keyboard and I respect it.