I don't see a problem with 1" if you don't have a huge fat ass... my ass is pretty lean, bubbly, but lean... 1" gets it in far enough without causing any problems. It depends on the person..
The problem with 1" is if the needle separates from the hub--it will be difficult to retrieve. Use 1 1/2 " for safety--you NEVER insert the needle up to the hub anyway..if you are doing this with 1", then you can get into trouble.