The highest total average is Dragon.
>this is what the rankings are per the official statistical average per type/element:
1. Dragon (517.83 = combined total average of all the stat criteria such as health, attack and defense)
2. Steel
3. Psychic
4. Ice
5. Fire
6. Figthing
7. Flying
8. Rock
9. Electric
10. Dark
11. Ghost
12. Ground
13. Water
14. Grass
15. Normal
16. Poison
17. Bug (371.65, source: Bulbapedia)
Source
However, speed is beaten by Electric & Flying, attack by Fighting, sp.atk by Psychic and defence by Steel & Rock. This I found out by comparing all types.