While I don't find a 4" GP100 too heavy or too difficult to conceal, I understand the preference for a somewhat lighter 3".
The new Colt King Cobra is very enticing, beautifully finished with an exceptional out-of-the-box triggerpull in the two that I've handled. My hesitation on them is two-fold: 1). I'm uncertain if Colt is now using thorough=hardened action components; if not, future action jobs are limited to spring swaps. Older Troopers/Lawman/King Cobras used surface-hardened key components...; 2) Colt's viability as a manufacturer who will still be on the scene 5 years from now, as the perpetually seem to be on the ragged edge of bankruptcy and insolvency.
Ruger's 2.75" (or rarer 3" USPS version) Speed Six would be my best recommendation. Even though Ruger no longer supports them, they're so well built that they rarely break or require servicing.
An expensive alternative would be Chapuis Manurhin's MR-88, which is a French refinement of the Security Six, and still available BNIB, in 3" and in stainless steel.
https://chapuis-armes.com/en/manhurin
If having the best sights available is a vital criteria, I'd suggest a Ruger Wiley Clapp GP100 or one of the 3" GP10s0 with Ruger's adjustable rear sight-or the lighter, half-underlugged 4" GP100 Match Champion (or a 4" Security Six)
Best, Jon