Hi Danny,
What type of meats/food will you be smoking?
If it is primarily butts and brisket flats or points, you would probably be OK with a #1.
But once you start trying to fit several racks of ribs in the smoker, you are most likely going to want at least a #2 or maybe even a #3. I love being able to fit an entire rack or ribs in my #3 without having to cut them in half like you would have to do in the #1/#2.
I have a #3 and for the most part could have gotten away with a #2, but I have now had smokes where I have filled the #3 to the max. I don't remember ever reading anyone here wishing that would have purchased the smaller of the models they were considering. Although, now that I say that someone will perk up to prove me wrong
You can always smoke less in a larger smoker, but not more in a smaller smoker. So, I say go as large as your budget will allow. For me it was between the #2 and #3 and I justified the #3 because this is a 20+ year smoker, not a 2-3 year smoker like the cheapo's that I had been buying. These things are built to last.
That being said, I think you will be very happy with the Smokin-It brand of smoker no matter what size you choose.