Ti can be plenty stiff, carbon can be extremely comfortable. So, setting that aside Ti's appeal to me is mostly practical:

1. There's no paint to scratch on most Ti frames.
2. Cable rub or other small scuffs can be fixed in five seconds with Scotchbrite if your bike is finished like mine. Available at Target.
3. Apply a little Pledge (also available at Target) and you have a shockingly new looking bike, even if it's 20 years old.
4. I can toss it in the back of my car without treating it like it's made out of eggshells.
5. Metal frames like Ti almost always use standard round seatposts and standard clamps. This design is the best to work with: easy to buy parts, easy to get the saddle dead-on straight and no risk of slippage.
6. You don't need to worry about cracking the frame by overtightening a seat post clamp or bottle cage. Ti is extremely tolerant.
7. Cool "pinging" metal sounds while shifting or from cable snap.
8. Ultimate crash resistance.
9. Try to find a carbon frame with a threaded BB that's not a mega-buck Italian brand.
10. Go ahead: clamp the top tube or seat tube on the workstand if you must. You're not going to crush anything.

Steel's even tougher than Ti but it rusts without paint. Stainless is even more expensive. Still, I crave a 953 bike.