For new players looking to Start 40k, here are my listings on which armies are best for learning the core of the game...
The best intro army is drum roll.........
Space Marines! just the vanilla kind leave all the extra flavors for another time...
They are the best from my point of view, they hit on all the core rules of the game and are very forgiving in the face of armor saves and Leadership tests.
In all new players don't need to start with space marines, i started with Imp Guard cause i like the big tanks... but space marines would have been easier to learn with.
if you have an opinion... lets hear it!