ばいいCan, Should, It'd be good if

たほうがいい dan ばいい sama-sama dipakai untuk memberi saran. たほうがいい berarti langsung 'Kamu sebaiknya...' atau 'Sebaiknya kamu...'. Sementara itu, ばいい memberi nuansa 'Kamu cukup...' atau 'Kenapa tidak...?', yang bisa terdengar lebih bersahabat, tetapi dalam konteks tertentu juga bisa terasa agak memaksa. Berbeda dengan たほうがいい, pola ばいい sering dipasangkan dengan のに untuk mengekspresikan 'Akan baik kalau (A), tetapi (A) tidak mungkin dilakukan'.

ないほうがいい is used to advise against doing something, similar to 'You shouldn't…'. It's a common expression that reflects the speaker's personal or subjective opinion. In contrast, ばいい suggests doing something, with a nuance like 'All you have to do is...' or 'Why don't you just...?' Unlike ないほうがいい, ばいい is often paired with のに to express 'It would be good if (A), but (A) isn't possible).'

Both can be used to give advice or suggestions, but the tone differs. ことだ sounds more formal or authoritative, as if stating a rule or guideline. In contrast, ばいい is more casual and conversational, often used among friends. Additionally, ばいい can be used in contrary-to-fact suggestions, such as 行けばいいのに ('You should go but you won't'). ことだ cannot be used this way.

All three expressions share the base meaning of 'it would be good if (A)' and can be used to express wishes or give suggestions. たらいい・といい tend to sound stronger or more assertive than ばいい, which feels lighter or less serious in tone. While often interchangeable, in questions like どうすればいい？・どうしたらいい？ ('What should I do?'), といい is not usable.

When followed by いい, both ば and と express 'if you do (A), it would be good', but with different nuances. ば conveys uncertainty and is used for unlikely events, e.g. 'It would be nice if (A)', implying that it probably won't happen. と is stronger, often implying hope, e.g. 'I hope (A) happens.' Depending on context, といい can also suggest 'You should (A).'.

はずだ indicates something is expected based on information or logic, as in 行けるはずだ ('I should be able to go.'). ばいい expresses hope or a hypothetical good outcome, like 行ければいい ('It'd be nice if I could go.'). One is based on reasoning, the other on desire.