I've been improvising for over 13 years and every time I go into a scene I don a new character with a new voice and physicality. Some of my characters are similar to each other, but I create a persona that is unique for the scene that I'm playing in. I take this same approach to voice over in that I don't have any stock go-to characters. The copy inspires me through my personal experiences and reflections which invokes a physicality that produces a unique sound for the read. This may sound like a cheesy cop-out answer, but I truly feel I can play any character that is needed for the part.
My stronger characters for voice over high are younger sounding, high energy, and unique sounding.
For accents and dialects I can do Russian, Scottish, Indian, Appalachian, Texan, and Latino.