I'd go with the RC8. AE seems to have the hot hand at my track lately.
I think of the RC8 as an improved less radical version of the Losi 8. This car is plenty durable it just had/has some bugs that needed worked out. Get the service pack from AE and a new fuel tank and your set.
I can only comment on the RC8,8, and the Mugen. Though I did own an Ofna speed 9.5 ( I'll never go Ofna, Hao Bo every again. Beginner junk! Can't find parts. The Ofna was just sloppy.) I'm so biased against Ofna/Hao bo that I'll refrain from commenting more.
The 8ight is the fastest car I've seen yet. But only marginally faster than the RC8. The RC8 runs just as well and is more consistant. Thats why they're winning here. The 8 is a maintenance nightmare but parts are cheap. The 8ight is also the best for electric conversions I've seen.
The Rc8 can be settled down so it deosn't bounce around like the 8. The Silver state set-up makes a huge difference to the way the car jumps and handles the rough stuff. The RC8 is the lightest, smallest feeling nitro buggy I've driven. It lands jumps better and handles lighter than the Mugen. (After the silverstate set-up, particularly the #14 pistons with 2 X 1.1mm holes added in the shocks)
The Mugen is a tank. Its totally indestructable. I can't believe what I've seen this buggy go through. It can't turn or jump as well as the RC8. The Mugens brakes aren't nearly as good as what Losi/AE are running. Unless there is an upgrade I haven't seen. (The best brakes I've felt were all fibreglass like rotor material with steel pads. No extra brake pad glued to the steel pad. Both the RC8 and 8 are like this. Every Mugen I've driven had steel rotors and two piece pads.)
I don't judge these cars by "out of the box set-up". Each car has obvious faults that are so easy to fix they're not worth mentioning.
I decided to buy the RC8 recently.