Many factors to consider for what would be the best shell for your circumstances. I shoot side by side shotguns in all guages but the 20 and 410 are my favorites. Next I hunt over very skilled GSP's (I have 3 of them). The birds I shoot are stocked pheasants, wild woodcock and wild ruffed grouse. I find I kill many birds with (20g) 2 3/4" low base shells but in brass, seems the nickle expands enough to make shell removal tough. I do use the 1 oz loads with max dram powder. In the second barrel I'll use a 2 3/4" high base of the same load or a 3" high brass max load. Now for the size, 7 1/2 are my choice after 40 plus years bird hunting these are the most versatile with 6's being next choice. The 7 1/2 let be prepared for the the errant woodcock or grouse that may flush. Hunting over steady pointing dogs means 90% of my shots are within 20 yards and the shells don't tear the bird up. As for cripples well thats just frosting on the cake when you send the dog on a retrieve and they have to track and bring the bird back so that is not an issue for me. As for wild birds I've hunted Iowa, Nebraska, south Dakota and North Dakota. These areas I use all high brass and drop to 6 and 5 shot max load. Friends refer to me as a farmer because I only use side by side shotguns.