that's a tightrope, and only you can decide. There's diminishing returns for size vs performance-- And I mean by a large magnitude.
for example, I helped air someone up not long ago in a parking lot. He had a compressor the size of a beer can spazzing out on the ground beside his tire. He said he had been inflating for over 30 minutes. Tire still looked totally flat. I hooked my smittybilt 2781 (the opposite of small) up and aired it up in 30 seconds. And I had to let some air out to bring it back down to a proper pressure!
before that I had a canadian tire special that I carried around for years that would eventually fill a truck tire, but the hose shot off it when I really needed it most, and it totally let me down in the dark, on a highway, after a day of roofing. I put my faith in a POS emergency compressor. Lesson learned.
I'm sure some viair users will have some good recommendations. My contribution is: don't go too cheap - even if it is for emergency use