I like negative bonuses. I help about a dozen kids roll up 5e characters every day at my Summer camp job. The other day I saw a couple roll 18s but was much more jealous of the one who rolled the ultimate in rarity, a 3 (at four d6 drop the lowest that's a 1 in 1296 chance). I mean that's something to roleplay. And if there's not going to be substantial variance in bonuses there's little reason to have bonuses.
Now I do think the game would be streamlined if we used, say, a 2d6-2 score generation method, made the score just be the bonus, and just adjusted to always having positive bonuses. Translating scores to positive and negative bonuses (the things that actually matter) is an unnecessarily cumbersome system that only still lives because of tradition. Mathmatically adding 2 to a d20 roll to hit 20 is the same as subtracting 3 to hit 15 and addition is slightly easier than subtraction for most people so maybe an all positive bonus system is better. But I want the possibility of some bonuses being very low.