Heroes 3.

I would recommend The Shadow of Death if the choice is between it and Armageddon's Blade. In The Shadow of Death, you can play on maps generated by the game itself, while I remember that you can't in Armageddon's Blade. In general, I recommend playing with other players right away, rather than with the AI.

Actually, it's the exact opposite. If you install The Shadow of Death, there will be no random maps. But if you install Armageddon's Blade and then The Shadow of Death on top of it, then random maps will be available. But there may also be various bugs... + you need to replace the executable file with version 3.2 to play online.

Therefore, I repeat once again that, in my opinion, it is better for a beginner to play the complete collection. Install it and play. There will be no headaches.