What it means
ばよかった expresses regret about a past choice or situation. It means that doing something would have been better, or that the speaker wishes something had happened differently. It is formed by adding よかった to the conditional form of a verb. The familiar form is used in ordinary informal speech, while ばよかったです is a polite counterpart.
Usage note
ばよかった usually refers to something that was not done or did not happen in the past. It is different from a simple recommendation because it looks back on a completed situation with regret. Do not use ばよかったでした; the polite form is ばよかったです.
How to use it
Verb (conditional form)よかったです
昨日、薬を持ってくればよかったです。
I should have brought medicine yesterday.
Verb (conditional form)よかった
昨日、薬を持ってくればよかった。
I should have brought medicine yesterday.