http://speakspeak.com/resources/english-grammar-rules/various-grammar-rules/apostrophe-d-had-or-would In the phrase 'd better do something (used for giving advice or warnings) 'd = "had". You'd better be careful - it might be dangerous there. = you had better We'd better ask someone else because I'm not sure. = we had better But : It would be better if you came on time. ( условное придаточное, где есть свои подлежащее и сказуемое) Оба варианта правильные))))

It would be better if you came on time.

это вообще условное наклонение

I would be better if u come on time