Twinkle Park-Sonic Adventure
I like the way you drive the car so then you can reach the castle and go to the top of it passing through the whole Kingdom, the stars effect is a nice adding.(I know it´s just a park)
Metal Harbor-Sonic Adventure 2
One of the only levels I can keep running without having to jump on things that slow me down, also the addings to the level like the jets and the rockets add a nice effect.
Emerald Coast-Sonic Adventure OR Windy Valley-Sonic Adventure
Emerald Coast is nice because it looks pretty real, the sea effect and the footprints are also great, plus it doesn´t look like a level made specifically for you to pass it.
Also windy valley because it has 3 different parts that require 3 different gameplay style:
Part 1: Aiming, control while in air and ability of not to fall. This level holds shortcut knowledge, a bit of speed and air aiming.
Part 2: You just keep jumping on springs, just try to aim well to them. This level holds air aiming.
Part 3: Need an exelent stick controlling for you not to crash with the 2 rails that stop you from falling. This level hods speed.
At the end we become so good that you won´t even notice it, bad most of them have glitches that will allow you to clear level without using the normal track, like with Tails who is able to pass the whole Windy Valley in 40 seconds touching floor only once!
I don´t really like overpowered levels with overpowered music, but I acept other people´s opinions.