I have tried RL-19 in several calibers from my 243 up through my 7mm RM. THe better loads were in the 26-06 up. It just seemed a bit slow for the smaller ones.
That said, I used it for my 162gr loads in my 7mm RM and it was awesome. It also worked very well in the .280 I just gave my nephew for Chirstmas with the 139gr Hornady SPBT.
As a favorite, well I can't say I actually have one, except for RL-22 in my 25-06 using the 110gr Acubond or the 115gr Partition. That is simply the best overall powder for that rifle.
Work up slow with RL-19 in the 7mm RM and you will find it does a great job with the heavier bullets. If your getting the velocity but not the accurasy adjust your seating depth a bit, and it should come right in. I know several folks who ause it and they all are getting good velocity with excellent groups out to 300yds.
Mike / TX