My absolute, hands-down FAVORITE ruler is my "Wrights EZ" ruler, 6-1/2x24. I love that ruler and use it so much I bought a second one. It's really easy to read and the size is super handy. I also have a handful of square rulers made by this brand, in various sizes. I buy them at Joann's.
I also like Creative Grids, and the frosted Olfa rulers. Oh, and my June Tailor strip cut rulers. I think my triangle ruler is Fons & Porter and I use that one a lot too. In general, I like rulers that are clear or lightly frosted, with thin black marks.
I do NOT like Omingrid/Omnigrip - all that yellow and green makes it really hard to see where my fabric edge is. I also don't like the "Cutting Edge" rulers that are supposed to sharpen your blade as you cut - I bought one and it DULLS my blade. BOO!