Point buy
But theres no reason not to include both in the book.
Also would like to see some common arrays already made, like 4e had.
Actually, although I've advocated a standard array as an option, the array I've suggested actually
isn't just a pre-made array. If you work through all the costs, you'll note that my preferred point buy gives 28 points, while the array I suggested gives
29. (And, as others have painstakingly worked out, the 4d6-drop-lowest method is roughly equivalent, on average, to about 30.5 points.)
The reason I've advocating building in that sort of a disparity is that there's then a trade-off - if you go with point buy you have less raw power, but you get the opportunity to optimise it more fully than a standard array allows. And random rolls give even less ability to optimise, so again they get a (small) power break.
For that reason, I wouldn't advocate having many pre-made arrays, because if you provide more than a couple the chances of getting "the array I would have built anyway". Still, I could certainly see a case for building two or three arrays in this manner, and especially if the designers make sure to make them slightly sub-optimal (by including a couple of odd-numbered stats).
(Oh, one other thing - if including both random rolls and point buy in the system, it's important that both are at least viable options. 4e failed in this regard - the point buy system was quite clearly superior to rolling, both in terms of optimisation and raw power, and in a system where stats were already too important to leave to chance! 3e does quite well with the trade-off between 4d6dl versus 25/28-point buy - that's obviously not the only possible arrangement, but it is a decent one. The key thing, though, is that if you include both, they should give comparable results!)