EDITOR'S OPINIONTroy Baker always excels at playing devil-may-care, slightly rogueish and snarky characters, and since Sigma is just that, he's a really natural fit for the part. It should be noted that in order to preserve the twist of Sigma actually being a young man in an old man's body, Troy only voices Sigma during the game's promotional OVA, rather than the game itself. While I understand why he doesn't do the voice in the game as well, I do think it's a shame we never got to hear his voice as Sigma in either of the games proper.
Jamieson Price briefly plays "Zero" Sigma as a hologram during one of Virtue's Last Reward's most chilling scenes, and he sounds great. Price is normally known for playing roles that range from hammy and boisterous, to reserved and sinister, and while it is kind of an obvious choice for the role, hiring him to pull off the latter this time around definitely lends a very haunting presence to Zero's brief appearance.
I feel that it's not totally right to think of Matt's performance here as simply a Troy Baker impression, since if I had to go out on a limb, if he was the original VA I'd imagine his performance would probably sound like this to begin with. Plus he actually was the one here with the most material to work with. But regardless I feel that if they are considered as "impressions", Matthew Mercer's Troy Baker replacements tend to work best when he's talking normally, and since ZTD Sigma is his much more reserved self, the effect works pretty well for the most part. It does waver a bit as an impression during Sigma's rasher moments, and his voice is a bit smoother than Troy's slightly rough texture so the change is noticeable to the trained ear. But as a performance on its own merits, he gets the job done, shows off a more remorseful Sigma who lays his emotions bare, and actually manages to bridge the gap between the two actors pretty well.
Overall I'm going with Troy, but I do appreciate what the other two actors bring to the role.