Depends on your needs and riding style.

I would normally be riding approx 43 cm c-c bars. I like training on wide bars (went to 44 c-c and 45 o-o for a while) but I am currently using 43 o-o bars. I prefer narrower bars so I can thread tighter gaps in the field. 40 c-c are just a bit too narrow.

In the winter, my square bars are 44 o-o, 43 c-c, so wider. Training on wider bars is nice.

Lemond, not a "shouldery" kind of guy, rode 46 c-c for a while. We all went for that look, emulating him, but it was like trying to steer a motorcycle. That was when I tried the 44s. I went back to 42s for a while, then eventually to 41s.

cdr