Owner of both savage flux (converted to XL) and Traxxas Slash here; I love both but the Slash is more durable (although you WILL break either if you’re doing it right). You can’t go wrong with either, both absolutely MAD fast, Flux is more of a spectacle due to its size, but the Slash is the slightly more sensible choice (if there is such a thing) whilst still being batshit mental fast on 3S (12.6v) lipo batteries. To make the Savage truely fly 5S or even 6S is phenomenally, ridiculously, hilariously overpowered, and therefore both great fun and also self destructive.
As for Nitro and Petrol powered, not my thing. Noisy, smelly, dirty and very high maintenance puts me off. Especially the noise. It’s not a good noise, like a V8…