For range of cogs, I'm still fine with 8-sp in this area.
The 9th, for me, is the 11t, and the 10th, for me, is the 21t or 23t...
So as far as range goes, 7 and 8 are more than enough.

For smoothness and reliability, I'm an 8-sp guy. I like the thunk.
My smoothest, in order:
8-sp Shimano 600 STI
9-sp DA STI
8-sp DA STI
8-sp Ergo (Chorus)
9-sp Ergo (Chorus)
8-sp RX100, Sora, RSX, and 9-sp Ergo (Mirage), 7-sp RSX

The main affecting variables, in my experience with the above:
Matching RD, cassette to the shifter.
RD adjustment. RD adjustment. RD adjustment.
Ergo's seem to like a little lube and the RD's need to be clean and lubed.
Shimano seems to tolerate lack of maintenance much better.

10-sp? My only 10-sp is Dura Ace 7800 down tube shifters, running a full 105 set, otherwise.
Works great, and the $300 I saved buys another bike. It's a century bike so I anticipate more and hammer less.

Like USAZorro, I'm waiting for the price to drop on some stuff, but given the quality of the C&V bikes that can use the older stuff, I doubt it will happen for a while.