Tough to say. My personal statement was rather personal and gave me lots to think about. I didn't major in bio, chem, etc. so maybe that could be a factor. I did very well in grad school and have been doing a ton of research with publications so that could also have had a little to do with it. My ECs weren't spectacular but they were meaningful to me and I think I was able to convey that well during my interviews. I also improved my MCAT score a lot the second time, so it is possible that adcoms saw that in multiple areas I was able to improve myself.
Honestly, I'll never know for sure what made me stand out. But I like to think that the aforementioned improvements did me well.
Come time for your interviews, be sure to know your app well and be able to relate to your experiences, especially as they fit in with your pursuit of becoming a doctor. The pieces will fall into place. A good MCAT score always helps!