16ga for me as well. Smaller lighter frame is why I prefer the 16.  
 
Regards,
   EXACTLY, 12ga. framed drillings are tanks, and even though i've owned a few, they are just too big/heavy to carry for long, at least for me they are.  If you have a nice petite 16ga. drilling, it will be a joy to carry and hunt with, and if you are worried about 16ga. ammo being available, you can make your self a set of these, 
   slide them into your 16ga. chambers, and shoot all the 20ga. ammo you like... 
  Once in place, your drilling works/acts just like it did with 16ga. ammo... 
  DM