What is the best trigger for a tactical CQB type AR? Is a single or two stage better and why? Which brand is best?
Thanks

Unless you are shooting an scoped AR with a free floated barrel and match grade ammo, you don't need a 2-stage, or any of the "match" triggers.  A CQB/open combat/HD/SHTF AR should have the mil-spec trigger/FCG in it.  The standard mil-spec fire-control group is the most reliable and the most rugged, not to mention least expensive and easiest to repair/replace.  So, basically, what ever came with your AR (if its a factory gun, but if not, a mil-spec FCG from a reputable manufacturer/dealer) would serve you best.  

Mil Spec semi auto fire control groups Hmmm, me thought Mil Spec is Full auto, or 3 round burst.

I prefer a single stage trigger for a duty/field gun. I use an JP Enterprises trigger with the 4LB spring (3LB seems a bit light for a duty/field gun). Many people swear by the Accuracy Speaks trigger also.

If you must go 2 stage, then I understand that the KAC 2 stage is one of the finest available.

Did the JP drop in or is there a little fitting required?

JP did require fitting. And being somewhat of a perfectionist, it took me about 4 hours. It probably could be done in less than an hour. They provide great instructions, and a video (They are available for help on the phone too), so it is not too complicated.

Accuracy Speaks is the basic same design as a milspec except with tighter tolerances, smother surfaces and no creep.  Single stage.

It's good for CQB and precision shooting.  Best of both worlds.