It seems to me that whatever is "HOT" from the big name shooters, is what everybody is thinking about and buying. Pac Nor and Shilen "were" at the top of the list for a long time. Lots of folks are of the "I want it now!!" group so if the wait time is shorter than some of the bigger name barrel makers, that's who gets the sale. Over the years I found out that Douglas as well as E.R. Shaw are very good barrel makers. Not as much heard about them but, they have been around for a LONG time.
I hesitate to mention Green Mountain Barrels because if the word gets out about the quality and speed of delivery, they'll be falling behind in trying to keep up with the demand. And they have also been around for a LONG time.
The only problem with the "drop in" barrels is they may not be the exact specs you're after. That's why I order to "MY" specs. That way I can't blame anybody else for mistakes in building and chambering my barrels.