I agree with your assessment that Miller is the better goalie BUT, in fantasy terms, MAF still plays for the Penguins. That being said, to me their fantasy value is basically a wash, so you'd be giving up Sharp to get an older goalie on a worse team, but it seems to be your favorite team.
I would tell him Miller for MAF 1 for 1. He gets a goalie of equal value who is 4 years younger on a better team. I have their value being very similar but I give MAF the edge honestly.