You can't downgrade the iPad unless you have saved SHSH Blobs for the version you want to revert to. Since you are just starting your journey, there is absolutely zero chance you have those, so you should probably stick with 5.1.1. It is likely to be the last version of IOS for the iPad1 (unless Apple provide any maintenance releases after IOS6 is out), and is definitely the best 5.x firmware for that device.