I've been riding on 700x23 Conti GP4000 ($65-70 per tire) on my Litespeed for several years. Switched to Conti GP 4 Seasons ($70-80 per tire) last year.
My Felt that I bought in October 2011 came with 700x25 Vittoria Zaffiro Pro tires ($35 per tire). I'm not surprised that the ride is more comfortable but I was surprised that my average speed is faster than on the Litespeed with the 700x23 Contis. And I haven't had any flats either. Flat protection was my primary reason for buying Conti tires all these years.
So I purchased a set of 700x25 Vittoria Rubino Pro Tech tires ($35 per tire) for the Litespeed. I picked Rubinos because I had them on my commuter bike in 2001-2004 and only had one flat during that time.
If both brands offer good mileage and excellent flat protection then $35 per tire vs. $75-80 per tire is a no-brainer.