Here are some extra Community Builds mentioned in the comments!
Slipstream Package by StarkMaximum: Extra Slipstream, Slipstream Bounty, Ring Boost, and Collision Boost

Spin to Win v2 by SeaToon: Spin Drift, Collision Boost, Extended Slipstream, Mini Ring Thief

SlipBoost by Deltaray3012: Slipstream Bounty, Extended Slipstream, Ring Range Up, Ring Boost, and Mini Ring Thief OR another variant of this by StoneyHalfDragonHero: Ring Thief, Ring Gain Boosts, Extended Slipstream & Slipstream bounty.

Comment and I might add yours!

"No one is using Handling Cars."
Time Trialers: "Hold my Drift."

1:56 Mario Kart DS players: Snaking? I haven't heard that name in a long time...

“The extreme gear is very easy to push around since it’s so light” meanwhile me, playing Zavok in a full power car being slammed into a wall or off track by sage or cream in extreme gear

There's a build called Drift King? You know, they used to call RT Game the Drift King back in college. So, now we all need to convince him to not only play this game, but this exact build as well.

"Means you get ice physics" I do not believe this. The ice track feels 100% worse than sand, technical drift or technical drift on sand.

The reason you dont see many acceleration vehicles is because acceleration is useless. Just charge a level 1 boost and you are instantly back at full speed

Zavok: "Its not about winning, ITS ABOUT SENDING A MESSAGE!" (bomb barrage)
Sonic: "Jesus Christ Zavok! This is a chill race with friends!"
Zavok: "No peace in KART RACING rodent!"

Power cars are really good for ring builds. You don’t lose rings when hitting walls, and it makes up for a lack of Defense items. It also causes players who collide with it to lose rings.

Id argue that every bumper cars build needs a ring thief gadget. Even mini thief can go a long way. Since the speed difference between 99 and 100 rings is so big, keeping everyone from hitting 100 is a huge deal. Combine that with everything else that makes people lose rings during a race, and you find people rrally struggle to catch up with you...especially if you combine ring thief with collision boost.

One of my favorite combos is the slipstream package (Extra Slipstream, Slipstream Bounty, Ring Boost) with Collision Boost. You catch slipstreams faster, you get rings during them, the rings make you faster both from game mechanics and the ring boost, the slipstream makes you faster, and then when you catch up to them you can ram the back of their kart, knock them out of the way, and boost forward to get past them. It's a great way to ladder yourself up out of the pack and try to frontrun. I would recommend a defensive gadget for the last slot like 130 Ring since you're trying to stay ahead. If you want better defense, you can swap Ring Boost to have an extra slot for Crash Pads, since the slipstream rings and collision boost will probably get you going fast enough.

If you want to get all A ranks in timetrials to fill out your jukebox:
Starting Boost bounty, ring gain boost, drift charge kit. With a speed character and a speed car. Swap to a handling car for super sonic speed. Easy and consistent.
For online:
Extended slipstream, slipstream bounty and ring speed boost. This gives you two slots to flex. You can swap to mini ring speed boost if you want to add in a 3 slot gadget like drift charge kit/quick recover. This won't help you frontrun like a silver surfer build or try to cheese out a win by bagging, but it does make you very hard to dislodge from the top 3 positions making it good for the legend grind.

Lvl 1, 2, 3, 4 Charge with Silver in Handling is also pretty fun. Make every corner, get boost.

Honestly my prefered build these days is exceedingly simple. Hyper Ring Engine, 130 Ring Limit, and Ring Doubler. Just boost all stats to 100 and get rings as fast as possible.

For Handling you could do Handling character, Handling Kart, then Drift kit, Lv 3 charge, Ultimate Charge. Or at least that’s how CallieMacN got to Legend 1.

I think the biggest thing to take away with this game is that there really isn’t any one true best way to play this game. Unlike MK8DX and MKWii which have all the professionals use the exact same builds, SRC doesn’t have such a build; simply put, it doesn’t exist. Or rather, it does theoretically exist, but there aren’t enough slots on the Gadget Plate to actually use it in the final game (unless a mod comes out, but that’s an auto-ban right there).

handing cars are the meta now lol

A couple notes. The higher drift meters dont make you faster. they make you just as fast as level 2 but they last longer, but since they also take much longer to charge they are actually slower (hence why some players spam level 2 drifts). Also level 4 drift doesnt make you invincible by default kyou will notice this if you get it from the drift frenzy). It will only make you invincible if you get level 4 drift from the ultimate charge gadget or handling vehicle kit gadget

The problem with acceleration machines is that the only thing they have going for them is maximum traction on sand or ice, which there are a total of... 3 maps, if I'm including a Crossworld map. And that's it. Acceleration-wise, due to a secret vehicle mechanic, they actually accelerate slower than Power machines on Sonic Speed and overally the whole acceleration stat feels very underwhelming. All of this combined makes every other type of vehicle simply better. Sega honestly needs to give acceleration cars something, because otherwise you're just intentionally shooting yourself in a foot if you fancy yourself a nice-looking car.

The build I've been currently using is one I feel works on all Machine types, except Boost.

Slipstream Bounty, Extended Slipstream, Ring Range Up, Ring Boost, and Mini Ring Thief.
Feels especially nice on Power and Speed sets, since the Ring Thief plus Ring Boost acts like a slightly lesser collision boost