I would offer the opinion that "no-brainer multi-bagger" is an oxymoron, or perhaps some exotic species of unicorn only visible to the febrile imaginations of hotcopperites.
If truly only 1 stock? Imagine if was your super fund. No recreational factor - Telstra. Communication isn't about to go out of fashion, so even with (more) bad management, there's be something like 2/3 capital salvage.
1. Look for upside. 2. Look for a warm inner glow (very consoling when it goes belly-up, truly). 3. therefore pick your favourite biotech - my current fav. is Allied Healthcare Group (AHZ, formerly BioMD/BOD). Last year it was Avexa/AVX.
Discl: holding buckets of AHZ/AHZOA, a few AVX. Not holding TLS.