Mack has been the better player this year but overall this is/will continue to be Makar.
Part of why Mack has been better this year is because Makar is playing through an injury that has limited his mobility just enough to make him a little less effective then we are used to seeing.
But assuming that injury recovers(Which to be fair is a decently large assumption), he'll be the best player of the two.
Strictly based off of right now, you probably take Mackinnon. But especially if we're talking about what player to build around like OP suggested, Makar is the best choice.