最好是

zuìhǎoshì
(as a complete expression, or followed by 啦 la) (coll.) Yeah, right! As if!

CEDICT

colloquial

Entry Composition

1 最好 zuìhǎo
  1. best
  2. had better ...; it would be best to ...
=2 是 shì
  1. to be (followed by substantives only)
  2. correct; right; true
  3. (respectful acknowledgement of a command) very well
  4. (adverb for emphatic assertion)
=2 是 shì variant of 是 shì