Well, not to point out the obvious, but the i5 is faster, has more SSD space and costs more.
I first bought the i3 but became frustrated with little things - the occasional lag and stutter, slowdown in keyboard entry when typing in a blog such as this one, and especially running queries in my Access database. I also grew tired of being paranoid about watching my SSD space.
I went for the i5 and am glad I did.