I have the 18" Mag and love it. My current setup is Edelbrock Shorties > Stock Cats > Mag Y-Pipe > Mag SI/DO 18" that exits behind the rear tires (No Res).
It has a nice tone to it without being too powerful. When I have a splitting headache it really doesn't bother me.
Personally, I wouldn't go with the 22" Mag as MangoTangoMofo suggested but he hit it right on the head that sound is subjective.
My buddy had a 14" Mag (No res) on his truck and it was nice but if you were in the back seat, you couldn't carry on a conversation.
Everyone has their own taste. My dad thinks my truck is over the top loud and I think it isn't loud enough but don't want it to be permanent so I am looking into another cutout.
I'm sure that either way you will be please and if your not, just do it over