They are all really good. The worst ones are the majority of season 2 and the beginning of season 5. Some of the better ones are,
season 1:
ep. 8
ep. 9
ep. 17
ep. 18
ep. 22
season 2
ep. 1
ep. 2
ep. 4
ep. 6
season 3
ep. 7
ep. 10
ep. 13
ep. 16
ep. 17
ep. 18
ep. 21
ep. 22
season 4
ep. 3
ep. 10
ep. 13
ep. 15
ep. 19
ep. 20
ep. 21
season 5
ep. 6
ep. 13
The rest is all just fantastic episodes of Nathan and Haley starting with season 6