If your ultimate goal is a particular jet airline, do you know what that airline's minimum command hours requirements are? Once in most airlines, you will do five or more years in the RHS which is long enough for them to know your suitability, so whether you have 500 hours prior command, or 5000, probably makes little difference to your promotion prospects.
Meantime with a choice, unless you are way short of minimum command hours requirements, look at the respective operators. Is the B1900 operation some small and obscure GA outfit with little in the way of a formal check and training structure? Presumably the Dash 8-300 operator is quite substantial.
Another consideration : Does the B1900 operator use simulators for initial and recurrent training? The Dash operator is required to by law. Jet operators will be interested in your prior exposure to simulators, and in fact without this you may struggle to make it through their selection process.
A prospective jet employer should be looking at your background. Better a F/O who has come from a structured, reputable operation than a Captain from a cowboy mob. This is not to say your B1900 people are cowboys, but a lot is in the perception.
Good luck.
Last edited by Mach E Avelli; 4th Dec 2012 at 19:23.