Well, I'm going to be the one that goes against the flow here. I don't feel that the 10" gives any real advantage of the 8" wheel. It isn't large enough to make a significantly higher grind line and it misses out on a couple of nice bits the 8" gives you.
Starting out, the 8" wheel was the easiest wheel for me to grind on, hands down. I've tried just about all of the common wheel sizes out there from 4" to 14". Anything under 8" can get hard to learn on because it's hard to stay on the wheel. The wheels over 8" get difficult because the groove that you make with your initial grind is shallower and harder to stay in. Don't get me wrong, I love the 14" wheel and I use it all the time, but it's not as easy to start out on as an 8", and neither is the 10", imo.
The 10" wheel will give you a shallower grind, which may be better for some, but not to me. The 8" wheel makes a nice, deep hollow on thicker stock, if I want a shallow grind I'll use a 12 or 14" wheel or just flat grind it if I don't want a hollow at all. On 3/16" stock and thicker, the 8" wheel makes a nice, deep hollow (although the 4" and 6" are more drastic).
My other argument for the 8" wheel is that it is about the largest size that you can reasonably use for grinding in curves (handle curves, blade sweeps etc). Even the 8" is a bit too large, but it's workable in more situations.
The 8" wheel is not my favorite wheel, nor is it my "go to" wheel, but if I could only have one and I had to pick 8 or 10, I'd go with the 8".