Which is better for a beginner?

So I'm saving up for a camera and there are a few camera options and I don't know what camera I should get and I don't understand any of the differences? I'm sorta an advanced beginner. So what cameras of these? And if you have any suggestions for a good cameras? And under 700 perferably

sony a55
nikon d3100
canon rebel t21

I would get the canon rebel t21, my friend is in the photography club and she told me that she LOVES canon cameras