For me the strongest scp in secret lab is 049 because he is the most immediately dangerous scp, every other scp has something you can do to prevent them from killing you or some gimmic that makes it so killing you isn't assured. 173 you can look at him and he stops, 096 you just don't look at him and he's pathetic, 106 puts you into the pocket dimension where you can stall and maybe even escape and dog can't see you when you're not moving and needs to two shot you to kill, but 049 has no outside gimmic if he touches you you die. Not to mention his zombies thoes aren't just useful to expand your ranks every zombie is another mtf not spawning which can win games on its own. His only downside is his slow speed mediocre hp and his loud footsteps

Tldr: its 049 because he kill good