The following work well for me:
Bedlam - named undead (Sir Patrick, Lady whatever, etc)
Labyrinth - Minotaur and Miasma (others are rather difficult, but reptalons and Pyre work as well)
Blighted Grove - Thrasher, Coil (for best results. Abscess works as well, but is very difficult)
The Citadel - anything.
Painted Caves - Troglodytes, Lurg, Grobu
Twisted Weald - Changelings, Irk, Spite, Guile, Lady Llisith, Silk, cu sidhe, Swoop
My best luck per effort is Troglodytes and best luck per time spent is Miasma.