No one martial art is superior to all others. Just like the most convincing theologians study a mixture of religions, the most effective martial artist must study a mixture of martial arts.
I started boxing when I was 14, then added Muay Thai when I was 16, so I definitely agree that Muay Thai becomes much more effective when you can punch, since a punch is, in general, a faster attack than a kick, and since I'm 6'1", it's got a long reach.
But, since joining the Army and getting a good job within that organization (...), I've come to realize that Krav Maga is probably the best 'art'. I use quotes because it's not an exact form (like say... karate), but that's one of its greatest strengths. It incorporates the elbow/shin/knee strikes of muay thai, as well as the grappling element, with judo-style throws, aikido-style joint locks, and other really debilitating maneuvers that can end fights pretty quickly (I like the lunging elbow to the sternum...).
So if you're looking for pure lethality, I'd go with krav maga. It's really good for me, because when I box, I'm a righty, but in a traditional, 'hands-up' muay thai stance, I'm a southpaw. Since either stance works with krav maga, it's easy to adapt to whatever combat situation I find myself in.
In other words, I vote 'other', lol.