Bolts or screws?
If you are concerned about the durability of the screw/bolt itself, it depends on the material they're made of.
You can get hardened 2mm with oxide layer, good luck breaking that. You can also get cheap zinc coated one-timers that will be useless after 2 tightenings, because the head will be an unusable mess afterwards.
If you intend going for screws rather than bolts, you may have issues with keeping the thread in the material at that diameter. The durability of the thread in the material is poor as well, you get very few in/out cycles with a screw.
Bolt runs through a nut, increasing the overall complexity, but reducing above drawbacks.
I usually use AISI 303 or 304 stainless steel bolts, they're the most common stainless ones you can find.
There are also variants with hex or philips heads. Hex is awesome if you can hide it in the design (heads are more bulky).
They are cheap, buy some of that stuff and test it, you'll find your preferred kind pretty soon
But yeah, for bolts, the 2mm is a sweet spot. Below that you don't get much benefits, and they are considerably more costly. 3mm is much more bulky and takes up a lot of space in tight places.
I personally avoid screws for anything else than wood.