Also tandem wise I am looking for comments/opinions on 9 spd vs 10 spd (shimano mainly).
We have two tandems with 9-speed and one with 10-speed. All have Shimano STI, and the 10s two-fer shifts at least as well as the 9s bikes. IMO, ten speeds make sense if you value closely spaced gears. I like it because we can now have a 12-27 cassette that doesn't skip the 16 tooth cog like the 9-speed 12-27s did. On the other hand, if your bike has an 11-32 or 34 cassette and it's all the same to you, why bother? It may be "state of the art," but you'll still be stuck with 2-tooth jumps in the most-used range.
As for chains, I have stuck with Shimano and had good luck. Do like Wipperman and KMC quick-links, though!
We have Shimano 10sp cogs. I like the Wipperman nickel plated 10sp chains. (The nonplated chains tend to rust.) However, I use the Superlink connector. We had a Wipperman connector break but never had a problem with Superlinks.
We tried a DuraAce chain but the new ones are now too narrow for our 9sp crank. I measured it at 5.9 versus the Wipperman 6.0.
The general thrust of opinion is that 8spd chains last noticebly longer than 9spd and 9spd
longer than 10spd. Since the main difference between 9 and 10spd cassettes is in where
the single step (for 11/12t to 23/27t cassettes) or double step for 32-34t cassettes begins
to jump up to multi tooth steps, unless you are very sensitive about this there is no real
advantage to the change from 9 to 10 cogs. 10spd chains with quik connex links have all
gone to one use links, or for Shimano, continued the use of one use pins so expect to pay
$1-2 for each chain break with a 10spd chain. There seems little reason to "upgrade" to a
10spd setup unless forced to by a bike change. Another development worth considering
is the charge to 53-39-30 triples led by Shimano, but rapidly being adopted by others for
the same reason: it duplicates the double CW set up of 53-39 and reduces the manufacturing
costs of having two separate forging lines, one for triples, another for doubles. If you like the
42t CW stick with 9spd, as long as they are available.
Co-Motion Supremo Tandem, Co-Motion Periscope Co-Pilot Tandem
We have 10-speed on both our tandems, one Dura-Ace, one Ultegra. Both with SRAM chains. The only noticeable difference we've seen with the 10-speed chains is shorter lifespan. We've broken 2 chains, one 9-speed, one 10-speed...both Shimano (not at the connecting pin), so we're using SRAM exclusively now. We do enjoy the closer spaced gears of 10 vs 9 (we run 11-23 or 12-27 depending on the terrain).
We started out with 11-32 and switched to 12-25 in June (9spd) and really
like the closer spacings. Our new bike has an 11-26 SRAM 10spd. Another reason
not to change to 10spd, if you haven't looked at the catalogs, 10spd brifters
are in the $325-450 range, compared with 9spd brifters in the $140-220
range. Cranks are priced likewise. Cassettes are a lesser premium.
RMAC thanks for the update re connex, but can they be used on KMC, SRAM
and Shimano or Campy ie do they make several widths or one size fits all?
FWIW: The ultra narrow (Blue Card) links won't work on Campy's 5.9mm 10 speed chains... Well, that's not entirely true. You can get them on if you try REALLY hard. However, they won't come back off. If you're running Campy 10 speed stick with SuperLink III Green Card or SuperLink II Pink card models.