三句话都是对的。只是感情色彩不一样。“请进来” 表示客气委婉一点。 “进来吧” 比较直接，跟同事，熟悉的人说。 你的问题“哪是对” 这句话有点问题，要说成“哪个是对的”。

All of them are right. But the moods are differert. If you were a boss, your employee knock at your office door, you could say all or ‘’请进“ directly. But we hardly ever use ’‘请进来“， it is a mouthful. Comparing "-进来吧" with "-请进来吧", the latter is politer than the former. When you talk to you friends yo could use the former.

如果对方是熟人（friends），一般是2 进来吧 如果你是在办公（working）或者不熟的人(someone you don't know well)来家做客，一般是1 请进（一般没有来） 一般不用3

Please come in. Come in. Come in please. Almost the same...

yes, they are correct