i've been using a cruiserweight (usually rosalina) w/ a variant of the mach 8 (mach 8, circuit special, sports coupe, gold standard), (cyber) slick tires, and whatever glider i feel like using, and it's been doing alright for me (if my rating, which isn't all that great imo, has anything to say about it).
this combo is pretty inefficient. you get more out of using super heavy + teddy buggy + slick + accel glider.
you get +0.25 water speed, +0.75 anti gravity speed, +0.25 weight, +0.75 traction, and +0.25 mini turbo while you only lose -0.5 handling. handling is hardly important so it's a very good trade.
unfortunately in this game, the super heavies outclass pretty much every other weight class. +2 speed and +2 weight >> +1 accel / traction / +2 handling / smaller body frame in some cases. metals are an alternative to super heavies if you're willing to trade 0.5 speed for 0.5 handling and a smaller body frame. there are also some decent combination with medium weights. you could try rosalina + standard quad + roller + accel glider for cruiser weights but it's not the best combination unless you're racing in dolphin shoals lol.
in terms of how important stats are: you want as much (land) speed / weight possible; at least 2 (3 is nice, 4 starts to diminish the effect but still viable with inside drift bikes) acceleration unless it's a top speed combination in which case you have to live with 1; mini-turbo helps offset the speed advantage if you're using a high acceleration combination but doesn't do it entirely; it's nice to have 2-2.5 traction so your combination is more consistent overall in the low traction courses but not 100% needed, and handling you can mostly ignore.
as for the other speeds, anti gravity speed is nice to have as there are a lot of tracks with anti-gravity, and some like both of the rainbow roads are mostly anti-gravity. water speed only noticeably helps in the notorious dolphin shoals (which is as matchup dependent as BW OU - a lot of the combinations that have high water speed also have high acceleration, good traction, and high miniturbo.) and a bit in water park while air speed should just be ignored.
my personal favorite combination is:
super heavy / landship / slick / weight increasing glider OR super heavy / mach 8 / rollers / accel increasing glider
not sure which is better but i've been leaning towards the former.
other good combos are:
2 accel fast: super heavy / teddy buggy / slick / accel glider
fastest you can get with 2 accel (5.25 land speed, 5.5 anti grv speed), 4.75 weight, sexy atv drift, decent traction and mini turbo.
very fast: super heavy / speed kart / fastest speed tires / weight glider OR super heavy / speed kart / gold/metal tires / weight glider.
former is slightly faster while latter has a bit more weight and traction. latter is more of a 'counter' vehicle: if the super fast combination is all over the place, the latter can bump that combination further. otherwise it's a bit worse than the former.
inside drift bikes:
super heavy / inside drift bike / rollers / accel glider
4.25 speed with 4 accel is cool. good mini turbo, great at turning, great at breaking from the pack, but a bit light.
super heavy / inside drift bike / slick / super glider
5.25 speed with 2 accel. traction is garbage.
there are some other good/decent combinations but i don't want to go too indepth now.