I'd say probably meth, closely followed by coke/crack. I have "wanted " coke very, very intensely during cravings, but it never had the "need" feeling that comes with benzos and opiates. Like, the very shameful, "I will eat any man, woman, or child piece by piece if they are standing between my sick ass and some methadone" kind of "need". The kind of need where it feels like the glue holding your bones together is rotting, and your veins are filled with rashes.
Benzos are by far the most physically addicting, but a kid who takes a week long meth/coke binge will basically be full blown addict stealing from his parents for $10, desperate for just one more. Benzos and opiates will never do it that quickly. Even a few hours into doing coke, you can have a responsible young kid doing creepy, sketchy stuff for money for more. It's scary fast.
Me personally, my anxiety takes away from the draw of stimulants. I cant enjoy a good speedball when all I can think about how sad my family will be when I die from a coke-induced heart attack. Opiates and benzos, however, really sunk their hooks in. I got on IV heroin in 2010 and I'm still on methadone 10 years later. I literally cannot imagine a life without them. So, for me, opiates. They give me everything I was born without, and maybe a little extra. That's a very alluring draw.