After multiple playthroughs and many, many hours, I've only just bothered to try Steady for the first time. It's amazing! You get 95% chance to hit in VATS from almost any distance. Suddenly, VATS sniping is a goer again. I just wish maxed-out weapon-skill-sniping had been a bit more like this in the first place (though obviously not as OTT as with Steady). The only downside to it seems to be that it doesn't last long; in the battle of Hoover Dam, I became addicted to Steady, Rebound and Rocket and was having to re-dose what felt like every thirty seconds.
But yeah. My new favourite chem. So... what's your favourite chem and why?