Based on the votes that have been cast in the "Rate this episode" threads of each episode I have worked out the average mark per episode and they are below in league table order. Episode 19 is still relatively recent and will probably change quite a bit from day to day but the rest should be pretty steady by now.

Rank - Episode - Ep number - Percentage
1. The Man From Tallahassee - Ep 13 - 90.8% (ave 9.08/10)
2. The Brig - Ep 19 - 89.6%
3. One Of Us - Ep 16 - 88.9%
4. Flashes Before Your Eyes - Ep 8 - 86.2%
5. Enter 77 - Ep 11 - 84.8%
6. Par Avion - Ep 12 - 84.4%
7. D.O.C. - Ep 18 - 81.1%
8. Not In Portland - Ep 7 - 81.1%
9. Left Behind - Ep 15 - 77.1%
10. Catch-22 - Ep 17 - 75.8%
11. Tricia Tanaka Is Dead - Ep 10 - 74.8%
12. A Tale Of Two Cities - Ep 1 - 70.7%
13. Every Man For Himself - Ep 4 - 69.7%
14. The Glass Ballerina - Ep 2 - 68.5%
15. Further Instructions - Ep 3 - 68.0%
16. I Do - Ep 6 - 65.4%
17. The Cost Of Living - Ep 5 - 65.4%
18. Expose - Ep 14 - 64.5%
19. Stranger In A Strange Land - Ep 9 - 54.4%

Bear in mind the rating system changed to a 1-10 system after ep 5 but I counted eps 1-5 as a 2-10 system.