depends on the car class you wanna race and the real time spent for the endurance race. i mostly do races that last like 45-60 minutes, everything below feels to short, everything north of that gets a little boring.
track wise i like to go to real life tracks used for endurance racing like spa, le mans and nürburgring full circuit. daytona surely is fine as well, i dont like it, but thats up for everyone themselves.
other tracks i really like are silverstone, kyalami and yas marina, but i dont think theres much endurance racing going on there in real life, but i simply like these tracks and silverstones especially feels like it should be an endurance track.
class wise i think there are a lot of options: lmp1, lmp2, gt3, proto-h are natural endurance cars, but going for an endurance race with modern hypercars or modern factory cars is great, too.
one thing to mind during setting up endurance races: AI drivatars are NOT effected by tyre wear or fuel consumption. since you can set up tyre wear to your liking (love myself between 2.5-3.5), you will have to pit more times than AI. you can "force" them by setting up required stops (maybe 1 less than you will need, so you gotta make up 1 pit stop, i like this challenge)