The answer is skewed slightly by aspects of seniority. If you are to follow 411A's advice, you are limited to operators who will accept direct entry left hand seat - which are few and far between these days. Freighters and operators in crappy places to live are the usual suspects.
If you are contemplating a move into a strict-seniority carrier, and plan to stay there (like a flag carrier - BA etc) then the earlier you can get in the better off you will be.
If that carrier fails, though, you will be dumped on the market without command time. (Which is what happened to me.) That can be really annoying, as it severely limits your choices.