My picks, state as of 15-09-2019. It's very hard to make a list, rather than just a group of best tracks, here's my try:
1. Skating Toys
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The best custom track in my opinion. Looks even more stock-like than stock Toys in the Hood tracks. A long track that required a lot of memorisation, knowledge about the game itself as well as about the track, a couple of blind corners, very difficult raceline that can send your car off in any moment and requires from the player full focus and control. The track provides various hood-like environments (skating hood, one house, a park) and a couple of obstacles here and there (vegetation, 2 nets, . That gives the overall feeling that a player has to fight with himself and the track/ground itself in order not to fall where he/she shouldn't or not to flip/spin rather than finding paths between many obstacles and avoiding them. Very well looking textures and vegetation. Only downside of the track is some glitches on the edges, most if not all of them reappeared after IO meddled in it and added a reverse version. Definitely my favourite.
2. Spa-Volt 1
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Hard to say what's better in the track itself: the graphics or the racing line. This is a very well looking track: the environment, the walls, the details, the textures themselves – all that is present and makes for a very good experience. The racing line is very challenging and requires a lot of skill and practice to master to navigate between walls and obstacles on the way.
3. Toy World Mayhem
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A very stock-looking Toy World track with amazing dynamic racing line, where turns go smoothly from one to another without compromising the need to actually drive them properly to make a good time and not hit the walls however one may want to.
4. Biohazard Factory
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An interesting track with a unique theme. Provides solid textures and visually looks fine. The racing line is interesting and requires some skill – a conveyor belt with a jump, alternative path above the liquid waste that requires precision and a couple of regular turns. The only major downside is the existence of a shortcut.
5. Chilled to the Bone
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No surprise this track got into my list, although could be placed also as place number 9/10. A slidy track themed in an icy and snowy environment. The snowy part is not plain sailing all the way, and the icy parts require absolute control over the car on icy surface and anticipation. Looks completely fine outside, the cave looks quite well, especially the lightning effect.
6. Metro-Volt
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The classics now, which could be all given the same place, but a list is a list. So the first one is Metro-Volt. A stock looking track not located in any of the stock environments? Maybe Metro? Why not – this track looks really well and provides a good piece of necessary skill to actually go around the tight and wider turns properly, like the opened metro part and the slippery surface part. A quite fast track mixed with some zigzags.
7. Jailhouse Rock
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Another classic, which - as all classics - gets it's popularity for a reason, which is their very good quality in all areas that are important in a track. What can I say about this track? Looks really well and is well-polished graphics-wise. The flow is very good and the racing line is not that simple to just turn left and right at the right spots, the track requires proper positioning and the turns allow the players to fall off the edges to they have to be precise, adding to the challenge it gives. Some of the turns allow for various fast ways of approaching them, not just one.
8. Quake!
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The graphics on this track are fine – nothing special about them, nothing bad too. Racing wise – this track can be separated into a couple of sections. One is the stairs and the simple, slightly bent straights, which aren't anything special or unusual, but every "step" on the ramp stairs has to be taken a bit differently and there is no single proper way to drive them, which is great. Another one is the two-way part of the track, a real challenge and roller-coaster if you get hit and if you are trying to avoid them or cause them. And the main core of the track: it's difficult parts, like the destroyed bathroom with a sloped jump and the absolute beast: the downwards bent right-hand turn in the destroyed room with PCs, which is always a challenge no matter how many times you practice it and you can always hit the inside or go too wide making it ruining your race/time with it as well as with the theoretically simple left-hand jump following it, also the U turn with the PCs and one desk lying on the floor is very well made.
9. Venice
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A fantastic looking track, a masterpiece that track creators can always take as an exemplar. The racing line is extremely dynamic and difficult with all the elevation changes, fast changes of direction and small margins of error to make while making the turns due to obstacles like water, columns or chairs. Always difficult to drive, satisfying to complete (as any of the difficult tracks) and always entertaining to drive around here.
10. Rooftop Chase/Rooftop Chase: Redux
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I wasn't so sure what to put on the spot number 10, as I had to pick from quite a bit of tracks, but I decided to pick Rooftop Chase or it's Redux version. The track itself looks quite stockish, similar to Rooftops, but rather in the day. Perhaps this track was based on/inspired by some old Re-Volt artworks and concept photos, I don't know, but definitely the ramps in the air, jumping from one roof to another and driving on the roofs in general feels like something that could be placed in the original game files. What I prefer in the original track is the staircase layout after the "triangles with vegetation" part which requires much more control over the car and allows to use alternative path around the whole pit rather than just wallbanging, and in the remake I prefer the newer pool section with the extended roof and easier jump without a forcefield. Other than that, the graphics are good, there are even graffiti on some of the walls, and the track requires for the player to control the car and make the turns accurately, otherwise you can hit a wall where you don't want to or you can fall off the roof, which provides a moderate, enjoyable level of difficulty on the track.
Honorable Mentions that didn't make it to the best 10 (alphabetically):
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Cake
Fiddlers on the Roof
Floating World
Grisville
Helios
Holiday Camp
Industry
Kadish Sprint
Molten Caverns
PetroVolt
Ranch
Rooftops 1
Sakura
Spa-Volt 2
Toy World Aquatica: Redux
ToySoldierz
Honorable Mentions, but placed/rated lower than the upper ones, I could say "class B" (alphabetically):
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AMCO Bitume
AMCO TT
Avalon
Christmas Special Stage by Crescviper
Donut Plains 3
Elkhart
Fools Mate 2
Freyja
Go Play Outside!
Hallows Eve
Harbor Lights
Holiday Camp: California Edition
Hull Breach 3
Hull Breach 3000
Images of Giza
Lunar
MineZcraft
Moon Dawn
Narrock Pass
Overground
Penny Racers - Caves
Radioactive Garden
Re-Ville
Road in the Sky
Road of Simplicity 1
ROAR 2001 Carpet Nats
Route-77
RV Temple
Shakespeare Library
Shoppe by scloink (Ye Olde Fun Shoppe)
Snowy River
Stagnaro
The Bunker
Toy World EX
Toy-World Aquatica
Waterfall
White Rose Chapel
YABBA DABBA DOO!
There is also many other good tracks that I even listed (overall divided to classes "A,B,C,D,E,F") in a .xls file in order not to forget about and don't lose track of them, but the upper ones are the best among the good ones.