I'm like many people here - tried Harbor Freight and the blades fit fine, but all of the ones I bought (2 pkg, so 4 blades) were horrible. 3 were completely dull and one was sharp in spots, so it'd cut dashed lines only. So I'm done with those! I also prefer 60mm blades and HF are the 45's.
I buy blades at Joann's w/coupons; or sometimes I find okay prices on Amazon or at quilt shows/expos. Blades are something I'm keeping a constant eye out for and when I find a good deal I stock up.
My philosophy is that life is too short to waste on things like dull blades. Plus I just love how slick and smooth a fresh blade cuts, it's very satisfying.