I'm just throwing my two cents in, and I'm not at all trying to stir anything up, but it seems like BeatlesAtTheirBest is making two separate points;
1) That the Beatles treated Pete Best poorly when they fired him, and
2) That the Beatles were at their best when Pete was in the group.
To the first point, I would say I agree, and even Paul has said (I'm paraphrasing) that they chickened out and left the job of firing Pete to Brian. I get the feeling, based on interviews, that Paul felt they could have been nicer about it and handled it better. They could have sat down with Pete and explained everything to him, instead of just having their manager tell him he was out. He seems a little embarrassed by it now.
As to the second point, yes, John said more than once that he thought the Beatles were truly great back in Hamburg, but I always had the feeling that what he liked about those days was that the were playing what he considered "real" rock and roll. He always resented Brian cleaning them up and putting them in suits. Notice that in the interview with John that BeatlesAtTheirBest quoted, John says they were great in Hamburg, then Brian polished off their rough edges. He doesn't say, "We were great in Hamburg, and then Brian made us fire our best drummer." It's one thing to say John thought the Beatles were at their best at a time when Pete was in the band, but it's another to say John thought the Beatles were at their best *because* Pete was in the band.
Leaving the issue of quality aside (let's just say for argument's sake that both Pete and Ringo were at least competent) I think the sad truth is that John, Paul and George simply didn't like Pete all that much. I'm not saying they *disliked* him, just that he never really fit in with the group, didn't share their sense of humor, didn't hang out with them, etc. So when George Martin suggested they get rid of Pete, the others didn't have a problem with it. It's notable that when George Martin expressed similar concerns about Ringo, the other three didn't fire him too. Instead they insisted that the Love Me Do track with Ringo be the one on the album. By that point (again, leaving quality issues out of it) they liked him. He'd become their friend, and would remain their friend even after the breakup.
If we step back and look simply at history, it seems that John, Paul and George preferred Ringo, for whatever reason. Obviously, they fired Pete and replaced him with Ringo. When they had the chance to fire Ringo (when George Martin didn't want him on Love Me Do) they kept him. After the break up John and George continued to use Ringo on drums for a number of their solo albums. No one ever went back and asked Pete to be on their solo albums.
As to whether or not the other three fired Pete because Pete was the most popular, I wouldn't be surprised if that was *one* of the many factors in their decision, along with talent and personality, possibly issues between Pete and Brian, or Pete's mom and Brian, George Martin's request, etc. My guess is that all of these things added together made their decision. But at least according to legend, didn't Ringo get more fan mail than any of the other three? Again, no one showed Ringo the door. And I like to think, perhaps naively, that John, Paul and George were smart enough to realize no band is going to get big if they keep firing their most popular member just because he's popular.
So for me it comes down to thinking that John, George and Paul may have thought Pete was an OK drummer, but they didn't have a strong enough personal bond with the guy to outweigh the negatives. They just didn't like him enough to keep him on when they found someone they thought was better.