Collectively I'd say Johto has the best average of which members I like most, but going by a Rate & Divide system I came up with, these are the results...
Kanto: 2.25 (Lorelei 4, Bruno 2, Agatha 2, Lance 1)
Johto: 2.75 (Will 3, Koga 2, Bruno 2, Karen 4)
Hoenn: 3.00 (Sidney 1, Phoebe 2, Glacia 5, Drake 4)
Sinnoh: 1.50 (Aaron 0, Bertha 1, Flint 1, Lucian 4)
Unova: 2.75 (Shauntal 4, Marshal 2, Grimsley 3, Caitlin 2)
Kalos: 2.50 (Malva 3, Siebold 3, Wikstrom 1, Drasna 3)
Were you to factor in Champions, however...
Kanto: 2.20 (Blue 2)
Johto: 2.40 (Lance 1)
Hoenn: 3.00 / 3.20 (Steven 3 / Wallace 4)
Sinnoh: 1.80 (Alder 3)
Unova: 2.8 (Iris 3)
Kalos: 2.2 (Diantha 1)