I usually play the Calloway Hex or Nike 20XI balls for better distance and slower meter. They run 350-550 credits which is a bit steep.
I received a free WGT Team USA Vapor Ball during the Ryder Cup. I used it when I ran out of better balls. I have used them for about a week now and they play really well. I particularly like the way they putt.
For 150 credits they are a really good deal with a really good feel. Try them.