I have a bit of everything. 1st ruler was a Fiskars 24" long and it is fine but wanted something smaller, less likely to move on me and the only 18" ruler I could find was a Creative Grids - LOVE IT! If I could afford to replace all my rulers w/ Creative Grids, I would do it.
I have one Omnigrid and do not like it - those yellow lines - it's just too busy. It's a 12.5" square and would be the first one I'd replace.