>>1702888
>>1703323
Agreed; can't go wrong with a coinboxer. Just be aware that King Mario is not in ranked top shelf very much for a while (see >>1643738). His prime time is in the late summer / early fall.
Other choices: Rainbow Pipe Buggy is on the 50 top karts list (see >>1634613). 8-bit Block Glider is also a top 50 glider on the same list, along with the 8-bit Super Gilder which is a little lower.
Collecting the discounted 70 ruby Miis is also a good idea, but as a beginner it is recommended to achieve overall top shelf D/K/G coverage first. Use regular high end top skill drivers (coinbox / boomerang / lucky 7 / banana) to stack the top shelf and use Miis just to fill driver coverage gaps.
It takes about 15-20 each of D/K/G to get full ranked loop coverage.
Helpful coverage optimizer tool:
https://coverageoptimizer.pythonanywhere.com