The Mossberg Premiers were based on their Model M pumps, they had a tang safety and the receiver was split about 1/3 down on the left side. The Savage Premiers were based on the model 25 and had a button safety in the rear of the trigger guard and the receiver halves were split through the top. I have probably seen about the same number of each - I would place the Mossberg slightly more common but I have not seen that many of either.
Mossbergs pumps were based on the Meriden Model 15; they acquired the design from Sear after WWI and made only a couple minor changes to it during their years of production. The patents for that design are in the names of Basil and Arthur J. Savage. For some reason Mossberg stopped making the Premiers for Wards and Savage took over, that had to be sometime before 1929 for the Savage Premiers to be based on the model 25; Mossberg stopped making pump 22's completely in 1931. The patents on the Mossberg design ran out about 1929 and if you compare parts with those of a Savage Model 29 you will see the basics of the design are identical.
