Hello and welcome to the forums
Well,it depends.
MBP costs more but has more battery life,better LCD and better build quality,whereas the other one is cheaper(I assume?)
What's your usage ?
I recommend you go with the i3 processor, since it is more powerful. Check out this guide on laptop speeds: http://www.microsoft.com/Windows/pc-scout/laptop-speed-facts.aspx. I think it will help answer any questions you have about processors.