The problem I have seen with point buy systems is as follows:
Using 25 (or 28) point buy, players simply won't consider certain character archetypes (notably any class with MAD, such as the Monk). Additionally, when constructing characters of other classes, they'll first identify the dump stats (Cha and Int for a Fighter, Cha and Str for a Wizard, etc) and assign 8's to these stats. The remaining points are then assigned to the remaining stats as efficiently as possible. It got to the point that the players might as well not have been there - had they told me their intended race and class I could have assigned the points for them with a greater than 95% level of accuracy. The bottom line is: characters become clones of one another very quickly, available options are reduced, and the game suffers.
To combat this, I tried briefly upping the point buy total to 32. I didn't want to go any higher than this because the game is balanced at about 25 points, and to play at a more powerful level I would prefer to just play at a higher level. The outcome was not the more rounded characters I had hoped for. Instead, the extra points were pumped into the same stats as the players had been emphasising before, leading to Fighters who were just as dumb and uncharismatic, but much stronger. So, no gain there, except that a player might very occasionally opt for a Monk (or would have, if Monks didn't suck, but that's another matter).
I have tried various semi-random character generator options. One, for example, used a deck of playing cards with only the Aces through Sixes present. Players dealt six hands of four cards, discarded the lowest card from each hand, and used that as their 'roll'. That didn't work terribly well - typically characters would end up with one really low stat, or a totally mediocre set of stats.
For my last campaign, therefore, I just used the standard 4d6 roll, and found that the characters generated were roughly equivalent to 31 point buy, but rather more organic than the simple point buy would have generated. It is, of course, entirely possible that I just ended up with a lucky set of rolls.
And yet, the characters generated by point buy are undoubtedly balanced (subject to the ability of the players to assign points 'well', of course). So, as I said in my first post in this thread, I don't know what the right answer is. Perhaps there simply is no attribute generation scheme that I will find entirely satisfactory.