It's much of a muchness. Plaza Premium might have a slightly larger variety of food, and perhaps of higher quality. I think the booze is not self-serve at Plaza premium whereas it is at Admirals Club.

Admirals Club looks better IMA but would be crowded betweem 7-9 PM as it's smaller and would have the MIA and JFK flights leaving close together, whereas Plaza Premium which now takes LATAM passengers would have its attendance more spread out.