For decades the rulers I have used the most are:
6" x 24" for cutting long strips, mitering borders, and helping to square up the long sides of quilt tops
6" x 12" for cutting shorter strips, subcuts, and just about any other task
8" That Patchwork Place Bias Square ruler for HSTs, squaring bu block segments, cutting snowball squares, keeping each round of a log cabin block square, etc.
12.5" square ruler or larger for squaring larger blocks, squaring up finished tops, etc.
Jan in VA