B and M. The smoothest coaster i've been on is wildfire at sdc. Every ride i've been on i have been jerked, hit my head, or violenty abused (boss). Thats happened to me on every coaster i've been on except wildfire.
Trim breaks are your enemy, retracking/smoothing is your friend. I miss b&m floored sit downs. coaster count=39
I'll go with B&M, they are very smooth for the most part. Medusa at GAdv, Hydra and Talon both at Dorney are some of the smoothest coasters I've been on. But Batman: The Ride has gotten a bit rough; but that's good, it makes it more out of control feeling.
However, like coasterguy77, I also think El Toro was the smoothest I've been on. They did pretty well making that steel look like wood [;)]
for me it would have to be just about any B&M I've been on, esp Griffon and Apollo's Chariot. However, I have referred to Titan at SFoT as "metal sex".
Actually Ricochet at PKD is RREEAAllYY smooth! Next time someone rides it notice how the first drop is like even smoother than Griffon's(AKA smooth as ICE).