Shifter/Troubadour or Shifter/Skald are both solid IMHO. They both work, and maybe Skald a little better.
You can't cast spells while shifted, BUT you keep chanting. You start combat with a cast of Nature's Mark or Hel-Hyraf, Shift, tear stuff up, return to Kith form to cast another spell/invocation or two (also when you want to switch chants), and pick your next form.
You can come out of Shifted form at anytime to cast some spells, and you have all 5 forms available per encounter. So, you don't feel obligated to stay in form at all. I was commonly hopping into Wolf shape to do a knock down, pound a few times, and switch back to casting.
Thematically you have a love of options. You have enough spell options between the two classes to make something for every element.
Corruption/necromancy type? Check.
Fire element type? Check.
Electricity type? Check.
Ice themed type? Check.
EDIT: Clumped enemies? Cast "At the Sound of his Voice" for a paralysis on them, and shift to Stag to get some carnage opportunities.
Edited by Ganrich, 18 November 2017 - 11:54 AM.