I thought this link was kind of interesting (even if it is a little one sided) & it kind of applies to the discussion. Bits and their Proper Use
Also, one of the girls on another thread mentioned something called an "eventing stop" which might be helpful to the OP if she decides to stick to the snaffle. You have tension in one rein and with the other rein you pull back like you would with a one rein stop. The idea is that it stops the horse with out prompting her to bend.