If it's an area you fly in regularly, try both of them, and use whichever one consistently gives you the best service.
If it's not an area you fly in regularly, try talking to some local pilots and see who they'd recommend.
I don't think there's much doubt that some LARS providers are better than others, and I suspect this is due to the workload of the controllers, which will vary from one location to another (and possibly at different times of the week, too???) But I doubt that whether it's civil or military makes much difference.
Might be interesting to post a similar question on the ATC forum - although the question might need re-wording so as not to offend anyone by suggesting that someone else is better at their job than they are!
FFF
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