I went from the AAir to the 36 DC and there is no going back. I got it because I got tired of wrestling the AAir into my hatchback... I am riding the SS 633 on a 105 cm GW mast in all wind conditions. So much easier to ride, lighter, less mass in front of you slowing everything down, easier to get into position on the water, much, much easier to waterstart with straps, hook(s), or strapless if you ever want (need) to do that. In general, if your goal is to stay on foil through all transitions (never touch down), then going smaller will be pure joy. If you want to do moves on the surface, you will have a lot less margin for error on the smaller boards. I just picked up a spare 2018 36DC as they are on sale prior to the 2019 36DC release which is identical except for color.
I am very interested in the upcoming Micro DC36, but if you ride a bigger wing like the 633, the mast needs to go ALL the way back. I need to see where they put the Micro track before I buy one. As per the image of the Micro on the SS site--which may or may not be the production final, it's 5cm ish forward of the regular 36DC which will not work for the 633 wing for me. It will work for the 590 wing very well, however.
In general, I feel like on a small board I now "ride the wing" vs "ride the board." Thus, smaller board-->better wing feel-->bigger hydrofoil sensation--->bigger smiles. Moreover, and much to my surprise, the smaller board felt EASIER from the very first reach. Case in point, my hyper-coordinated 19 year old son who has foiled maybe 20 sessions and was switching feet on-foil on session 3, already learned to sit on his board, doing tow-in with other kiters etc, thought my 36DC should be smaller for him. So, he picked up a free wake board, takes a saw to one end of it, cut it 6" shorter than my 36DC, Solarezed the cut end, sprayed Gorilla adhesive on the deck and stuck down a pad, drilled holes for his 633 mast and mounted with bolts from local hardware store. Size--tiny; Cost--$45. He loves it.
Lastly, get yourself a SS GW 91 setup. This has the 633 wing. Amazing wing. So fun!