For freestyle, I'd say the most used sounds are Roland. It shouldn't really matter what kind you use. I have a Yamaha DJX, a Roland D2, and software synths and I have no problem finding the right sounds.
this is my generalization based on yamaha, korg, and roland use in the past, i dont know it might be different to each person but anyway.
korg sounds generaly seem more natural/realistic when its acoustic you are looking for, such as grand pianos, violins, acoustic bass, etc. the classic korg M1 is a great example. maybe best for a funky acoustic natural groove approach.
roland has a more synthetic sharp sounds, esp drums, synth strings, artificial atmospherics. these are great for house, and freestyle, esp of the 80s variety if you want that robotic, techno/electro sound.
yamaha maybe in between, i dont know as much about latest yamaha developments these days. though yamaha keyboards are more on the synthetic side maybe.
It depends on what you like IMHO. All of those are reputable synth makers with good sounds. Watch out for older synths though if you want all the quality of the newer high quality samples. My advice would be to go to the music store and try them out and see what has the sounds that inspire you. There are also many good soft synths on the market today. Just use your ears to hear what you like!
you are all over looking some of the most popular synths used by dance-based producers of today, whcih also includes breakbeat and electonica... The Access Virus, The Clavia Nord Lead 3, the Novation supernova 2, the access indigo, novation bass station,...these are some of the tools of the trade besides the motifs', phantoms and Tritons. I have the Triton, Motif, and orbit 3 ,I also have and use the Supenova 2 to stack the sounds to enhance and give it an edgy feel, because everyone andtheir mom has the motif and Triton..I fu hear songs on the radio-u can tell right where it came from, so it's nice to have the higher end electronic pieces to change the sound up a lil.