Suggesting the Simple Answer
ばいい offers a solution, often with the sense that it is the easy or obvious one.
- 分からなければ聞けばいい。(If you don't know, just ask.)
ばいい vs たらいい
Near-interchangeable, with a lean:
| Pattern | Lean |
|---|---|
| ば + いい | a general solution — this is what works |
| たら + いい | this specific case — what you should do here |
たらいい is commoner in speech and slightly gentler. Both are ordinary.
Against ほうがいい
| Pattern | Force |
|---|---|
| ばいい | you could just — offering an option |
| ほうがいい | you'd be better off — recommending |
| べきだ | you ought to — a judgement |
ばいい is the lightest of the three. It presents the action as available rather than advisable.
The Wish Use
With a question or in the first person it becomes a wish:
- 明日晴れればいいなあ。(I hope it's clear tomorrow.)
And どうすればいい is the standard way to ask "what should I do?".