The "best" is a matter of taste. The standard scholarly trarnslation of Calvin is the Battles edition published by Westminster and retailing for $80 (often discounted to $50-$60).
I prefer the older Beveridge edition CBD sells for about $15-$16.
Battles is standard for referencing (and has some good footnotes). He takes a dynamic view of Calvin's words in some places. Beveridge is a little less flashy but is newly typeset in an attractive font that I find easier to read than the Battles edition. And, Beveridge sticks a little closer to the literal words of Calvin.