Kanto:
Lorelei - Decent enough, but suffered for lack of Ice-types in the first Gen.
Bruno - An absolute pushover. Two Onixes? Come on....
Agatha - Pretty cool, interesting personality, but like Lorelei suffered for lack of her speciality type.
Lance - Same as above, very few Dragon-types, but Lance is so cool that no-one cares.
Blue - Best champion ever, I think. A tough team to beat, and of course a great character. I liked the Champion being some-one you had fought several times already, it gave the game a real climax.
Johto:
Will - Interesting personality, fairly balanced team. Could have done with a Slowking and Espeon instead of Slowbro and the weaker Xatu. Would've made him more "Johto".
Koga - Nice to see him again in a different role, but again, Scizor and Weezing should've replaced Forretress and Muk. They just seem to fit his personality better.
Bruno - Again, a pushover. If he had had a Steelix, then he'd have been fine.
Karen - Great personality, and very sexy to boot. Question - what was she doing with a Vileplume? Gengar as well is overused. Should've had a Sneasel and Tyranitar.
Lance - Three underlevelled Dragonites - 'cos Lance is too cool for your rules!
Hoenn:
Sidney - Completely forgettable personality-wise, but had a pretty good team.
Phoebe - The opposite - Great personality, rubbish team. She should've had a Shedinja.
Glacia - What were they thinking putting an Ice-type E4 member in a region with only two Ice-type families in the whole Pokedex? Rubbish on every level.
Drake - Sorry mate, you're just not as cool as Lance, accept it.
Steven - Liked him. Nowhere near as good as the other Champions, but OK nonetheless. His team was pretty good too, Metagross and Cradily were evil to my team.
Sinnoh: (Based on Platinum)
Aaron - Nice to see an E4 Bug user, powerful Bug-types are awesome. Also, he has cool hair. I have nothing else to say.
Bertha - Like Sidney, completely devoid of personality. She doesn't even tell us why she likes Ground-types. Still, she has a shiny Hippowdon, so she gets points for that.
Flint - I'm saying nothing of his DP team, but his Platinum team was much better. Has a great personality, and even cooler hair than Aaron.
Lucian - Very annoying. Bronzong is not only irritating but incredibly ugly. A decent challenge I guess.
Cynthia - A good champion, her diverse team made for quite a challenge, and it was nice that she popped up several times before we battled her.
So to sum up, I don't know. Either Kanto or Sinnoh. Hoenn had the worst.