.enif si gnidaer tub ,sdrawkcab gnitirw dna gnipyt elbuort evah I
Upside-down is a bit easier for me. Typing / writing backwards, or upside down, just involves more thought than I want to put towards it. That, and it never really helped me out with anything. Reading backwards or upside down on the other hand, made it easy to read what someone is working on or looking at without arousing suspicion. Hah...I should have just typed the first sentence on the fly, then spell-checked. I think it would have gone more quickly in hindsight.