My understanding is that ほうがいいです is directly giving advice. For example, “you should eat more vegetables” would be もっと野菜を食べたほうがいです. Also, I understand that ~たらどうです hints at the same suggestive element except in a questioning form. For example, “why don’t you take medicine?” would be 薬を飲んだらどうです。Is there any key difference besides the inquisitive tone to the latter? For people who live in a Japanese speaking environment, are there certain preferences and sentiments that follow each one? ありがとうみなさん!