Hard to say, really.
First off, all DJI drones are suuuuuper easy to fly. Doesn't matter if it's a Spark or a Phantom. Flight control is the same. Above all else, if you get into trouble, release the sticks and the drone just stops. Also, read the manual.
As far as I know, both Spark and Mavic Air have "beginner mode" which slows things down, makes it even easier when learning. Or use Tripod Mode.
So: basic flight is the same.
An advantage to the Mavic Air that comes to mind is APAS, which allows the drone to fly itself around certain obstacles, no fancy flying skills needed. Additional obstacle avoidance sensors too. I guess that's more beginner friendly.
Mavic Air of course has many more advanced features which will let you grow as your photo/video skills improve.
Biggest advantage to the Spark is the price, as it can be had super cheap, so it won't hurt as bad when you crash it.
Things to consider:
What will you be using it for?
Mavic Air:
-professional video
-low light photo
-following fast moving objects
-anything you would want a dedicated camera for, in the sky
Spark:
-social media posts
-"for fun" YouTube videos
-anything you would use your phone camera for, but in the sky.
If you have no real interest in photography or video, and this is just a toy that you have fun with, then get the Spark. The fun factor is going to be pretty much the same.
Fwiw: I bought the Spark before the Air came out. It works great, meets my needs, easy portable. No regrets, and I don't feel the need to upgrade. That said, I do have a professional photo/video background, so if the Spark blew up tomorrow, I'd buy the Air.
Hope this helps.