Finally, remember that no engine is future-proof. They all evolve, or get abandoned. The projects you create within them, however, can last forever if you archive them properly. Choose an engine with an open format, so that even if it dies, your source files are readable and your game can be resurrected. A project saved in a proprietary, binary format is a time capsule that might never open again. The 'best' engine, in the very long term, might be the one that guarantees your creative work outlives the software it was made in.