A wise array of voices for all the random people in the game seems more important than getting "someone big!" for one voice.
For instance, I didn't recognize Liam Neeson in FO3, and all I got from Malcolm McDowell was "hmm, I think I recognize that voice".
Meanwhile, I'd prefer not to see something like this again:
Lynda Carter ... Female Nords / Female Orcs
Jonathan Bryce ... Male Argonians / Male Khajiits / Male Nords / Male Orcs
Catherine Flye ... Female Bretons / Female Imperials
Gayle Jessup ... Female Redguards
Linda Canyon ... Female Altmers / Female Bosmers / Female Dunmers
Elisabeth Noone ... Female Argonians / Female Khajiits
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I'd prefer actually voice actors.
In fairness, a number of notable actors do really good voice work. (Many of the people they got for the animated Batman & Justice League shows in the past decade or so, for example).