好久不见。
It's been a long time. *当别人这么对自己说时，通常用It sure has.来回答。

好久不见。
It's been so long.
John, is that you? (你是约翰吧?)
Yeah, it's been so long. (是我，好久没见。)

好久没见了。
Long time no see. *比较随便的说法。对方一般回答Yeah, how have you been?/Yeah, too long.
Long time no see. (好久没见了。)
Yeah, how have you been? (是呀，你还好吗?)
I haven't seen you for a long time.
I haven't seen you for ages.

还好吧?
How have you been?
How have you been? (还好吧?)
I've been all right. (嗯，挺好的。)

最近怎么样?
How have you been doing? *询问对方的身体和近况。
How have you been doing? (最近怎么样?)
I've been alright. (干得还不错。)

忙什么呢?
What have you been doing? *用来询问没见面的这段时间里的情况。
What have you been doing? (忙什么呢?)
Just working. (上班呗。)
What have you been doing? (忙什么呢?)
Nothing much. (没忙什么。)
What have you been up to?