Nobody's responding, so maybe a bump will help. Doesn't Optimum sell a smaller size? Like a 2.5lb or something? Why not try that first to see if you like it. I once asked on another discussion board if a certain brand tasted good and someone said it did. When I got it I thought it tasted pretty bad.
With that said, I know a lot of people think Optimum nutrition's protein powders taste good. Though I don't recall anyone speaking specifically about the Pina Colada flavor.
Personally I take EAS Simply Whey and I think the chococlate flavor tastes good. I'm gonna try the strawberry flavor next.