My issue with co.com is not so much a *A issue, rather that they seem to keep tweaking it and changing how it behaves. It lacks credibility, IMO, because it's shown me some weird stuff that shouldn't be possible.

Just in the last weeks, it's shown me standalone US segments in EasyPass only (then it will show them properly; then it will go back to EasyPass a few days later); potentailly illegal connections through other countries (AUA-EWR-YYZ-BOS); and so on.

We saw similar such behavior back in the SkyTeam days -- all of a sudden no AF segments would show. Then AF segments would show. Then only AF segments as part of connections, but not the same flight if requested standalone. Or domestic flights with Canada connections.

I think the appeal of ANA is that it's solid (what do you expect, it's Japanese!). It may not think of every connection in the book, and if the link is down to a carrier, it will say so (happens at times with UA or OZ, I've seen).

So I use co.com for CO metal searches with Elite status logged in; ANA for partner metal or non-Elite CO searches, and phone reps to book. It's a bit of effort to figure out the connection possibilities that ANA won't show because they're just a hair inefficient (e.g., SFO-UA-LAX-TG-BKK), but in the end, that's worked well for me.