Which concrete mix is better for these particular countertop dimensions?
Just being pedantic: PVA is glue; polypropylene is the term you're looking for. 

Cheng, in "Concrete Countertops" isbn 1-56158-484-3 states (p. 98) that Quikcrete 5000 is fine if you add fibers, water reducer, and pigments. If you don't already have the book, get it. 

As a general tip regarding concrete (or any mix-ables, for that matter), buy more than you think you'll need and be prepared to return excess. There's nothing worse than being in the middle of a job and realizing that you're short.