The Beatles remasters in 2009 were great. All Beatles CDs before then were questionable at best.
There are always exceptions to the rules but unless the original has abysmal production and/or mixing then you should probably stick with the original. But that’s just me. And you should always stay away from fan remasters.
Remastered albums don’t really alter the original master tapes; in fact, a lot of remastered music comes from the original masters when the previous copies either didn’t or were shoddily transferred. This is why the original CD release is rarely as good as the later ones. ZZ Top is a great example of this, but that’s a slightly different situation since they fiddled with the drum tracks for the 80s release, but restored the original mixes on the newest CD collection.