I'd pick the i5 machine if I was buying.
It's got a faster CPU, uses DDR3 instead of DDR2, and the hard drive is twice as big, for the same price.
Only thing the second one has going for it is a better video card, but honestly the 250 GTS is not THAT far behind and you can replace it easily when the time comes.
If you ever want to upgrade your CPU beyond this, the AMD machine might offer better flexibility in the long-term than a socket 1156 system. But realistically, an i5 ought to last you long enough that you'll be better off just building a whole new machine by then.