In 3.5 I would do all 18's - but as I learn about 5e, I feel like that's a less good fit, but I still like letting people be more powerful, so I might bump the point buy to 32 or something. Having all high stats never really broke anything, it just made everybody a little tougher, and it helped bridge the gap between the fighter and the wizard. They both got a boost, but the fighter got a bigger boost.