first of all, with pretty much all the 'newer' midi-keystations you don't necessarily need to use midi, it comes with a usb-cable which also works like a charm. m-audio keystations are very good indeed, go get one.
when you buy the m-audio card, you can run protools m-powered, if that's a plus or not depends on your daw-needs, but i'd say, you don't need it. the m-audio card is ok and reliable and i reckon the same goes for the ESI card, although i haven't heard of it before.
except for the brand name, these cards are pretty identical (as you might have already found out yourself), only the ESI offers you both balanced and unbalanced I/O which is probably useless to you.
you should check these reviews out to help you make your choice:
M Audio Audiophile 192
Meet Juli@, the new Sound Device from ESI - Product Reviews and Overviews - Home Recording Studio Help