[Shaun]

In terms of outlandish and instantly memorable casts (if not for the right reasons) I'd say it goes:

1) 6
2) 13
3) 10
4) 5
5) 8

7 was dominated by what I shall henceforth call the beigeoisie (Mikey/Imogen/Glyn/Jennie/Pete/Spiral/Michael/Grace) and only had a few fringe characters that made it worthwhile, 9 also had a dominant clique of interchangeable, awful bores, and the only other series that challenges the top five are 14 and 15, for all the wrong reasons.