Starting my villain arc

With Age of the Primes wrapping up and my collection including most of the 13 plus some additional Primes I'm looking at expanding my villain collection. I'd be grateful for some recommendations. I'm thinking:

Not Megatron or Galvatron, I already have those
From almost any part of the franchise except the live action films
Not corrupt Primes, I already have those

I have a few ideas such as Tarn, Nemesis when she gets re-released, Shockwave and maybe Magmatron. Who are some of the other villains I should be looking at?