Zac explained: "Some albums tend to be announced, released, charting, and then practically forgotten within a matter of days, so we’re trying to prioritize coverage on the ones with some staying power." Given a cut in the number of reviews, I agree with his theoretical explanation of Allmusic's priority. Unfortunately in practice, Allmusic hasn't been very good adhering to that explanation.
In terms of recording types, I'd prefer that Allmusic first prioritize reviews of original recordings (and reissues). There can be few exceptions to this first priority if a live album or cover/tribute album is exceptional. Even with original recordings