I regret to say it, but I prefer new school. It's just more logical. The old way only made sense in the sense of prioritizing Prime Requisites, but that justification dropped when the Paladin was introduced.
Partly due to 4e, but more because Dexterity and Intelligence seem like similar abilities. They're neuro network abilities and represnt how quicky and efficiently you have thoughts, make decisions and turn both into actions.
I would have probably opted for the 4e array. If there was one thing I would have kept from 4e, I would have probably kept that and the Fort/Ref/Will defenses with the choice of which ability to apply to which save (but give everyone proficiency in all three defenses.) The 5e saving throw system just seems a bit off in actual play, but I have never quite grokked why since it looks fine in theory.
And if I'm going to have a dump stat, unless I'm running a Cleric it's often going to be Wisdom so I can do gonzo entertaining stuff and still be in character.
Oh, and also intelligence has nothing to do with planning. In this edition, it covers: logic, education, memory, or deductive reasoning, making disguises, forging documents and casting wizard spells. You can be faulted for playing a well educated vulcan sherlock holmes with an intelligence of 5, but not for coming up with a good plan.
The easiest way to make int worth something... and to some extent charisma is using them in downtime activities. I think charisma is already used. If Int would be the ability you use for aquiring new proficiencies and languages it would be enough. Right now it is 250 days. If you make 250 days the default and reduce the time by 40 times your int bonus it would make high int actually very good. Allow a trainer to cut the time in half again and maybe add half knowledge (speaking only, half proficiency bonus) to cut it in half again and high int is probably never wasted.