The 3rd best Vacation
I didn't find this to be as funny as Vegas or European was. This would be my ranking:
Vegas had the best Audrey and the second best Rusty, the best Uncle Eddie, the second best Ellen, the third best Clark and the second best story of the series. European had the best Ellen, best Rusty, second best Clark and third best Audrey but had the funniest story. Vacation had the best Clark, the third best Eddie, Ellen, Rusty, the second best Audrey and fourth best story. Christmas had the second best Eddie, fourth best Clark, Ellen, Audrey and Rusty and the third best story. Vacation 2015 had the worst of everything.