Start at the original 26 episodes from 1995 up til the (controversal) End of Evangelion (1997) ending. Then, start with the Rebuild of Evangelion:
1.0 You Are (Not) Alone (3.5/5)
2.0 You Can (Not) Advance (4.5/5)
3.0 You Can (Not) Redo (4/5)
Side note: this is one of the few anime where it's okay to watch the anime/movies than read the manga. The story telling is jarring and very confusing at times in the manga, but on it's screen it's a bit less harsh.