I would definitely recommend trying some out at the show. I would go to my LA dealer's booth, and ask them to both demo rulers to you, as well as letting YOU "test drive" them. That way, you have the same "feel" as your machine and can try out several different rulers.
You may find that a LA dealer has a preference (if it's not their own brand, like HQ). Find out why they prefer a particular brand.
For me personally, I really like Lisa Calle's rulers. She has several different ones - circles, cross-hatching, curved cross-hatching and more. I have about 8-9 of her rulers. She also has a couple of DVD's out (both of which I have.)
I'm not affiliated with her in any way - I just love her products.