Oh boy. You just opened pandora's box. You are going to find that this question is going to be all about taste. Where some people may wind up agreeing on certain synths.
A true synth has no sounds to it at all. But gives you the ability to create whatever you want it to sound like. So your recommendations are going to be on what others prefer basically due to the stock sounds that have come with the synth.
My little suggestion is to stop by you local gear store and have them let you play with each one for a while and see where YOU fall!
"There are many more who have learned to be great than there are those who are born that way! Never stop mastering your craft" -Judah