It also kind of depends on where you'll be traveling. I have made several trips to Alaska and had a flat in the middle of nowhere Canada and if I had not carried a spare tire and wheel with me, the tire guy told me it would have taken him 3 days to get a replacement for me...that's how far out in the boonies we were. As it was, we were only stuck for 4 hours. Tire guy had the spare put on quickly after he got there, and off we drove a couple hundred miles to the next big town and found an industrial area with a large tire place. Bought a used replacement to carry with us the rest of the trip.
Now that I've moved up to 22.5" tires (from 19.5"), I'll get a used tire...that's 108 pounds. Worth the weight to me and basement storage space lost, considering the remote places I like to travel. With ERS, I won't ever be changing it myself, as a good tire truck service will be able to mount it on a wheel and my RV no problem.