We went with the 5qt and found it too big.
After less than a year of minimal use it began to smoke ..

S/N did replace under warranty -- however the replacement has gone ignored as a result.

Did notice they have this newer space saving stack model
https://www.ninjakitchen.com/ninjaus_hidden.doublestack

Get the bigger one.

Make sure you can slide at least a quarter sheet pan in it

Bigger always.

OP. I had not planned to leave the air fryer out on the counter unless I am using it (so I would think that means I can get any size). Is that impractical? I do not have a lot of extra counter space to dedicate even to a small one.

Ok this is what I love. What do you see yourself cooking in it and how much room do you have on the counter?

I am now a massive proponent of the Ninja Dual 10 qt. You can set it to smart finish you your potatoes are done at the same time as your chicken. I rarely turn on my Viking oven any longer and love that.

We only have kids home at school break but I find that I use the dual for a protein and veg 90% of the time.

Biggest one if you have space for it.

I’d like to get an air fryer. The Ninja comes in sizes 5qt and 6.5qt.

Spouse and I are empty nesters, so usually I am just cooking for two.

But, over the summer one kid is home from college, and the other kid works/lives in an apartment in DC but comes for dinner 1-2 times/month. I am not even sure if I’ll use the air fryer when all 4 of us are eating together.

What size do you suggest I get? Thanks.