I have some experience over the years of being an independent vendor / merchant (but not of knives). My favorites aside, if I was stocking a store I would start with no more than a dozen models. No one can carry everything and it is best to start with the common. So in no particular order here is what I would buy for stock. (Again not personal favorites but my idea of what sells)
Victorinox:
Classic SD - get a few different colors/textures
1 other 58mm - Rally, Rambler, and/or Midnight Manager
Camper - IMHO the most popular Vic SAK
Climber - Camper replace saw with scissors
Rucksack - Larger lockblade Camper
Farmer -very popular
Swisschamp - for those that are looking for everything
Soldier - for those that want the real Swiss Army knife
BSA logoed SAKS - at least one model, maybe two models, different ones than you are already stocking. This way you target Scouts, their parents and get more models for everyone else.
Swisstool - for those looking for a multi
Wenger:
Standard Issue - for those that want a "genuine" swiss army knife
Evogrip - at least one model (I would suggest either the 16 or 18.)
I know that on an order sheet there is more than 12 models included but hey,I cheat. Few of my current favorites or EDC made the list but this would be my purchase order. Hopefully you could expand your model line after a lot of initial success.
P.S. Smartknives is a SAK sight that lists knives by popularity based on those left at TSA checkpoints. You get a different list going that route.
P.P.S. Thanks for asking the question. It gave us a chance to not only stump for our favorite pattern but also got me thinking about mass market SAK appeal. Because if you are selling to the general public, your inventory should probably be different than if you are selling to SAK-aholics.