What do you mean by best vocals?

If you mean reaching those high notes, then Let's make it baby, Prayer, Does anybody really fall in love anymore are good bets.

If you mean a better tone and power it's Santa Fe.

If you mean a hard song that he nailed in studio my guess would be These Days, since those high notes come out of nowhere.

IDK, hope it helped.

If you meant live, then we got a lot more to talk about.