Who do I marry?

I’ve been in a relationship (not a great one by any means) with this girl for the past 6 years. It hasn’t exactly been a picture perfect one. In fact, most of the things that have gone wrong are entirely her fault (which she admits), so I broke up with her a couple months ago. We have briefly talked about marriage in the past, but nothing happened that was so spectacular that made me really sure that I wanted to propose to her (mainly due to the things she has done wrong)…

The same month, I meet a new girl who is everything that the ex is not. Pretty much picture perfect every single day. She wants to get married to me, and I instinctively knew rightaway that this is the girl that I want to marry. She is everything that I wanted my ex to be.

Now, enter the ex back into the picture… she’s been txting, emailing, calling me, and even showing up at my door all apologetic and claiming that she’s going to change and correct everything that went wrong in the relationship (I actually gave her a detailed list (let me know if you want to see the list in order to give me a better answer) and seems really sincere.

So what do I do? Do I give her a 2nd chance and possibly have her go back to her old ways (She has tried to explain how those things happened) ? or do I walk away from 6 years of history with her for the new one?