Well, you have to try out both, from what I read the ROLAND got good reviews on the Latin, and Korg has made available a free set of Mexican/South American Styles for the Pa500, Pa588, Pa800 and Pa2XPro Professional Arranger keyboards, I haven't heard the Roland although they tend to sound a little more muffled to me were as I heard the PA500 and it sounds really good. That's just my opinion, and like I said you have to try them both and see what fits for you.

Good Luck!
they are both good keyboards.