Hi Candy!  You should let your budget decide.  With that in mind, I recommend at least the #2, if you can swing it.  I have smoked a lot of meat in my #1, the sized difference in the #2 is well-worth the extra money!  I only smoke, mostly, for me, my wife and son.  But, that doesn't mean I only smoke one meal's worth of meat at a time!  A good vacuum sealer and freezer are a pit master's best friends! 

   The #2 allows you much more flexibility for bigger (in volume) items, like turkeys and briskets.  Any of the models can easily handle a pork butt.
Now, I really recommend the #3.  What the #3 allows you to do is, well, 
it all!  As has been said, you can always smoke less in a larger smoker, but you can never smoke more in a smaller one!  The #3 allows you to smoke whole racks of ribs, and full-length packer briskets!  You can still easily smoke just for 2 (as I do for 3), but when you need the BBQ real estate, nothing comes close to the #3.
Remember - this is a one-time, lifetime, purchase.  It will be the last smoker you buy; they're that good.  So, choose wisely, and get the largest model your budget can handle (except the model 4...that one would just be obscene for 2 people).  lol!  Bet I'll get some comments on that remark!!
Whichever way you go, you'll love it!  We're sure glad you found us, and we're here to help!!