The Mark II and Mark III are basically the same.
The Mark III is the newest version... It differs from the Mark II by having a loaded chamber indicator, a magazine disconnect, and changed from a European style magazine release on the bottom rear of the hand grip to a more common in the US style button behind the trigger guard. (though the button has become the most common around the world, the European style was big in the early part of the 20th century in Europe)
Both are good, but the Mark III is all you will find new.
They have several versions, from basic to tricked out fancy, and also a version with a more 1911 style hand grip/frame called the 22/45.
Another good option is the Ruger SR22 pistol. It is more modern and easier to disassemble and clean.
A 22 rifle was suggested as a good purchase in the future as well... the Ruger 10/22 can be had for $200 in the basic model. Lots of fun as well. Ruger made 25 round magazines are available for it, and are much better than the 3rd party versions.
Here is Hickok45's youtube. He has a lot of good info, and several videos aimed at beginners. He has a playlist of all his beginner videos. "Basics" and "Gun safety" are good playlists to start with.