What is the most potent or deadliest form
None of them until you've practiced for a couple years. Some get you to the point where you could seriously hurt someone else more quickly - if you're being offensive, rather than defensive. I don't think it's unfair to say that something like tae kwon do, simply because you can kick harder than you can punch, and because there's a greater range with kicks, will get you to the point more quickly where you can seriously hurt someone. However, if you were studying, working your way toward black belt, etc., with tae kwon do, you might be able to defeat people trained in other martial arts for a while, but by the time you got to your black belt, they'd pass you.
However, 90% of the time anyone, as an adult not living in a trailer park, gets into a fight is most likely going to be in a bar against someone who's drunk. Rule #1: You don't hit or kick drunks. And, with virtually any of the martial arts & 2 years of experience, you'll be able to put a drunk on the floor, in your control, and with your arm cocked back as you say, "don't start with me, asshole" without ever having to throw a punch. Keeps you out of jail that way, shows of your skills to the available females, etc.