I like the evenness that a point buy system for ability score generation can bring. You don't wind up with one party member whose highest stat is 14 and another party member whose lowest stat is 15 like you inevitably do when you roll dice. (Especially what with how there's usually one player in every group who can't be trusted to roll dice unsupervised.)
But randomness is fun, is I guess what draws people to the dice-rolling method of generating ability scores. Or maybe people just like it because it's traditional. (Not for nothing do we speak of "rolling up a new character".)
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A method that I've been mulling for many moons:
Roll 5 times, with whichever rolling scheme you like best: 3d6 or 4d6b3 or 1d20 or whatever thing you want to use (3d6 and 4d6b3 are traditional; 1d20 is for masochists; with this system, it shouldn't matter).
Then you set the sixth value to whatever number would leave you with the desired point buy. (If no such number exists, reroll the fifth one until one does. If rerolling the fifth one can't possibly make it possible to reach the target, roll the fourth and fifth until it's possible.)
Then you assign these six numbers to whichever stats you want.
Example: I just rolled 3d6s and came up with 9, 11, 9, 14, 14. If I'm aiming for 30 point buy (the value used whenever I DM), the last number must be 17, for an array of {9, 11, 9, 14, 14, 17}.
Example: Rolling 4d6b3s: 12, 10, 10, 13, 8. An 18 in the final stat would be a total PB of 29, so we reroll that 8, coming up with... wow, nice, 18. A final value of 9 brings us to 30PB, for {12, 10, 10, 13, 18, 9}.
Just for masochism, let's try 1d20s: 8, 6, 6, 14, 10. 18 would only be PB20, so we must reroll the 10. Except with those numbers it's not possible: if we rolled a 16, 18 would only bring us to PB28; likewise for two 17s; 17 and 18 (or 18 and 17) would overshoot, for PB31. So we must reroll the fourth and fifth numbers (the 14 and the 10), and now we get 15 and 16, which makes it possible to slot 18 in for the last number, for an array of {8, 6, 6, 15, 16, 18}. (Hopefully I don't need to remind you that this is something of an outlier because only crazy people roll 1d20 for ability scores anyway.)
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This method has all the interesting randomness of rolling, but the party still winds up balanced, stat-wise. You don't need to keep an eye on that one player who always suspiciously rolls really well, because his cheating ways will just net him a 3 in his last ability score or something (assuming you're using one of the expanded methods that permit you to go below the DMG-mandated 8), and all you need to do to keep him honest is double-check his PB math.
One downside: it's probably a little confusing, and probably many players won't be able to wrap their little heads around it. You may need to hold their hands. You may have to tell them to roll five scores by whatever method they desire, and then just do the PB calculation for the final score yourself. (Use a calculator.)