I voted for the 36" Deluxe. But that's only because I already have an 84" Deluxe with chargrill. I love the product that the 84" puts out. The warmer box can run hot depending on how you run your vents. If you want it as a warmer, what's worked best for me is to close the vent from the main chamber and open the top vents in the box to let the radiant heat bleed out. I use the warmer box for the sides I do for my event. It's a great place for half steam pans of baked beans or mac and cheese. I've also used it to smoke brisket while doing turkeys in the main chamber. Definitely go a size bigger than you think you'll need.
Smokin' BBQ for Good!
Lang 84" Deluxe with Chargrill; Custom Lang 36" Deluxe; BGE