Tough call.
Higher grade Colt double action revolvers like the Python usually sold more 6" barreled versions.
The problem is, Colt's that were sold as police guns like the old model Trooper and the Trooper Mark III MIGHT have sold better in 4" barreled versions simply because of the police sales.
My best guess is, due to the fact that police agencies didn't buy the 357 due to the cost, I'll say that the 6" version was the biggest production.
By what percentage I couldn't even guess.
Colt would know, but I'm not sure how you'd find out.