Each will only teach you about that particular platform. Building an AR wll teach you nothing about an AK. Then understanding the effects of shorter barrels on cycling and little things like that. Most won't make much difference to the average range shooter.
10/22s are pretty simple guns as they are. Most everything bolts together same as an AR. AKs can be built and are pretty involved but my understanding is that building is just as expensive as buying right now.
If you have little or no experience an AR would be the easiest. A 1911 would probably be a nightmare without a lot of help from someone who is very knowledgable. Same for an AK.
Get a real cheap gun, mosin, Hipoint, or something else that you won't mind tearing up. Take it home, shoot it, and try to fix things you don't like about it, and shoot it again to see if you got the results you expected.
What Tyoe of gunsmith work are you wanting to do, is there a particular platform or firearm you like?
I want to learn every thing about all of the platforms I mentioned. Just don't know the order I will do them in. The 1911 will be some what soon as i will be doing that instead of getting a class ring.