たらどう

1. 1Suggests or recommends an action for the listener to take.Ex. 1
2. 2Combined with てみる, it suggests that the listener try doing something.Ex. 2

Used in conversation to give friendly advice or suggestions to the listener. Plain たらどう？ suits friends and family, たらどうですか is the polite form, and たらいかがですか is more polite still. Compared with ほうがいい, it sounds softer and less insistent because it asks for the listener's opinion rather than stating what is best.

• はどうですかN5「はどうですか」 attaches to nouns or to a verb in its dictionary form plus の; beyond making suggestions, it can also ask for the listener's evaluation or impressions. When suggesting, it simply presents an option and asks what the listener thinks, so its tone is mild — unlike 「たらどう」, it does not directly urge and carries no reproach.
• ほうがいいN5For suggestions, 「ほうがいい」 is roughly interchangeable with 「たらどう」, but it sounds stronger and closer to advice, with a neutral register. It can also attach to the ない形 to mean “had better not,” or express a preference in a comparison — uses that 「たらどう」 does not have.
• といい / たらいいN4Beyond suggestions, 「といい／たらいい」 can also express a wish, and adding 「のに」 adds a nuance of regret; it can also attach to adjectives and nouns. As a suggestion it is softer than 「たらどう」, and it can also ask how to do something, as in 「どうしたらいいですか」.
• ませんかN5「ませんか」 attaches to the ます形 and is a polite invitation asking whether the listener is willing to do something (often together with the speaker), with no reproach; 「たらどう」 attaches to the た形 and urges the listener to take a certain course of action. For simply inviting someone to eat together or the like, 「ませんか」 is the better choice.
• ましょうかN5「ましょうか」 is used when the speaker offers help or proposes doing something together, attaching to the ます形 with ます removed; 「たらどう」 instead urges the listener to act, attaches to the た形, and can easily come across as rude to elders or superiors. When proposing a joint action, both can be used on the same occasion, but their tone and focus differ.

はどうですか follows a noun or nominalized phrase (コーヒーはどうですか, 散歩はどうですか) to put forward an option, while たらどう attaches to a verb and frames the suggestion as a hypothetical. ほうがいい is firmer advice, and たらいい typically answers "what should I do?" with a recommended course. ませんか is a polite invitation, often to join the speaker but also usable to urge the listener alone, and ましょうか offers the speaker's help or proposes a joint action, whereas たらどう is advice about something the listener will do.