"Double", "mega" and "family" roll are marketing words with no standard length. The useful number is total sheets or square area per pack.
Compare the total
Divide the pack price by the total sheet count, not by the roll count. Select-a-size sheets let you use less per task.
Tissues
Ply and softness matter more than box count if you use them near your nose. Fragrance-free is a common preference.