I have a Bisley Hunter that I like... A LOT !
I had mine worked on by David Clements and can't say enough good stuff about his work. I had a good bit more than a trigger job done, and turn around was exactly what he quoted at the time (8 weeks).
But for just a trigger job (and almost anything more) I would just as highly recommend Jack Huntington (JRH Advanced Gunsmithing), and he will probably have faster turn around time.
I recently sent my Redhawk to Jack for a trigger/action job and was totally satisfied with the job, the cost and the fast turn around (like 2 weeks).
He also did grips (fitted to my hand) and a frame mod on my Bisley Hunter.
As Cherokeetracker said above, I haven't touched the main spring on my Hunter (the hammer spring) but have installed a lighter Wolff trigger return spring. Theynbhave a couple different weights. I settled on the 40 oz spring, not the lighter 30 oz.
JRH - http://www.jrhadvancedgunsmithing.com/contact-us/
You will want to call and talk to Jack, he doesn't really do email.