That is the same question though.
The best place to run said service(ChannelsDVR), would be on what device offers the superior performance.
Though, in reality, would the average user notice any real world difference between those 2 devices, most likely not.
The only exception would be for transcoding and comskip, neither of which did user post to what extent they utilize those features.
What is "best" boils down to usage case. And can be relative.
To which, the user who asked, has not stated to what extent their usage of Channels DVR is.
Are they needing 4+ remote transcode streams, do they have several users, many live viewers, and remote viewers, many daily recordings...want comskip to run on all of them, and as fast as possible?? If yes to all of that, they you should get the most powerful hardware they can afford.
If your use case is one or 2 users, who maybe remote stream from time to time, and may use comskip but don't care it it takes a bit to process cause you don't watch recordings immediately after they finish recording,, then cheaper, less powerful hardware will be just as good for you and you have no need for super high end hardware setup.