Due to the expense of tungsten mainly, the average Joe is going to be more willing to purchase a copper-plated lead offering than the HTL or Fed HW loads for one.
12 gauge will out sell 20 gauge and every year when Wal- Mart has its equal #s of 4,5,and 6 shot the one that is always left is #4. Sixes out sell 5s in my area but not by much. Winchester has been a strong seller as well.
Just as the posts above state, rather than guess what they want just do a survey. There are many demographics to determine what will sell better. I applaud you for attempting to make choices available.
2 3/4" vs. 3" vs. 3 1/2" - more 3" in 12 ga.
20 gauge - #5 / #6 ( if available) 3" will sell better Win has only #4 and #5 while Federal has #6s