Let's just put this to bed nice and early. Baby Luigi was, is and always will be the best character in Mario Kart and that's just a straight-up fact. Truth be told, Baby Luigi and the Bullet Bike would rule all motorsport if they were given the chance to do so.
There is no debate, there is no close second, the Baba is the clear winner. First of all, the smaller characters are superior in every way. True racers will agree on that. The likes of Bowser or Donkey Kong are only for those who depend on their size as they try to fight their way through the riff-raff of the mid-field. The real drivers need not worry about that sideshow.
If anything, the smaller size is beneficial, leaving you nimble, elusive and adding to your ability to accelerate. Then when it comes to those smaller competitors, Baby Luigi stands out above the rest. Albeit he struggles to stand, given the fact that he is a baby after all. His voiceovers and mannerisms are more entertaining, his dress sense is on point and he's the cooler, more sophisticated alternative to the teacher's pet that is Baby Mario.
Baby Mario is a character for people with no imagination. Baby Luigi is the choice of the artistocrat.
The only character that comes any way close to him in terms of entertainment value is Yoshi. You can also enjoy Baby Luigi's innocence rather than knowing you are in bed with a villian, should you choose the adult Luigi.
If you disagree with me then be sure explain your choice on our social media pages and I will tell you why you are wrong!