I've never ridden Ti, but I'd love to...Anyhow, my ride is steel...I've rode aluminum and carbon fiber, and although they are lighter, I wouldn't trade by $400 ride for a $2000 ride (might sell it..but wouldn't trade it...then again, I could sell the CF/AL ride....???)
Anyhow, a good steel bike probably won't flex like that one fella said...I'm 220 and I can STOMP on mine and it just goes...
Around here, there are quite a few tar&gravel roads that I ride that my AL-ridin' buds won't...cause it vibrates their arms from their shoulders...I'm not saying it's plush, but it's not painful...and I get some new scenery...
If I had the dough, which would I choose?? the Ti...simply cause of the satisfaction of knowing you got something wicked...it's a little lighter, and most companies that put these things together are doing custom jobs...not just fitting you on what they got sittin' there...