ばよかった details

Examples

should have — regret over one's own missed action

もっと早はやく寝ねればよかった。

motto hayaku nereba yokatta.

I should have gone to bed earlier. casual

あの時とき、素直すなおに謝あやまればよかったと思おもいます。

ano toki, sunao ni ayamareba yokatta to omoimasu.

I think I should have just apologized honestly back then. neutral

you should have — reproaching another's missed chance, typically with のに

困こまってたなら、言いってくれればよかったのに。

komatteta nara, itte kurereba yokatta noni.

If you were struggling, you could have just told me. casual

The negative flips the regret: 買わなければよかった — "I wish I hadn't bought it."

たほうがいい
たほうがいい recommends while the choice is still open and can still be followed; ばよかった is the same advice arriving too late — the speaker regrets not having taken it.

ば
The same ば opening misleads — ば opens a live condition whose outcome is still undecided, while ばよかった is a frozen backward-looking idiom that admits no result clause after it.