Here's a collection of maps that I've personally tested and give an official seal of approval to. Everything here should be fun for races* or time trials. (Work in progress. QA for 260+ custom tracks takes time.)

Things that wont make the cut:
*Bad collision alignment (Can you get stuck? Do things that appear smooth or flat to drive on have hidden or unintentional walls that halt all of your momentum? etc.)
*No deathplanes, bad deathplanes, or deathplanes placed in an area that looks like it should be a valid shortcut. (If you don't want someone to take a specific path, place a visual barrier there or use checkpoints to prevent it. If you fall off the map and the recovery doesn't work properly or you can softlock yourself in a pit, you're gone from the list, etc.)
*Bad, nonsensical, or absent checkpoints.
*Tracks without music or poorly implemented music (too quiet, too loud, fades out without a proper looping point)

Newer maps still in development may see some forgiveness, but if your map was uploaded prior to the early access release of the game and still has issues by the time I play test it, it's going to be off of my radar at that point, sorry.

*NOTE: Most of my testing for these tracks have been in time trials. Expect that I'll have overlooked things like strange item box placement, bad or non-sensical waymarkers for AI drivers, and strange pathing for the tank item or anything that functions like it. Let me know in the comments if you had a bad time in the standard race mode and I'll take another look at that track.