Roark: 12 - 14
Gardenia: 19 - 23
Fantina: 33 - 36 in DP, 25 - 28 in Pt
Crasher Wake: 26 - 28 in DP, 32 - 36 in Pt
Maylene: 27 - 31
Byron: 37 - 39
Candice: 39 - 43
Volkner: 45 -48
I went over the levels of Gardenia's Roserade and Fantina's Mismagius (in Platinum). Mismagius is notorious for being quite tricky to deal with, and I personally had a bit of trouble with Roserade in my playthrough.
Hope I helped!