Despite the fact that Steel Bike is more suitable for a touring bike compared to Titanium because steel is stiffer & easier to repair, we should not look at the material of the frame when looking for a comfortable ride.
Remember, Comfort & Durability is more important than Speed & Weight.
Therefore, we should focus on:
1. Frame Geometry- the more upright, the less aerodynamic but the more comfortable. Consider frame with longer wheelbase like my specialized sequoia or Surly LHT.
2. A good saddle give you comfort. Im happy with my brooks saddle. Other 'high-tech' saddle like Topeak also give you comfortable ride but less comfort when paying $$$ for it.
3. Fat tires like the Big Apple give you more smooth & comfortable ride. Make sure the air inflation is right by considering the load that you are carrying.
4. The right bike like LHT or my folding bike, allows me to fix the fenders. this give me comfort when riding on wet roads
5. Proper gears like the granny allows you to climb with heavy load with ease. Butterfly handlebar also give your more space to hold on during long rides.
6. Correct Riding position especially when the bike fits you, will prevent body pain. Comfort = No Pain.
So, there you go. In order to get a comfortable touring bike, make sure the bike and its equipment is suitable for touring. Enjoy your ride!
Source: Sheldon Brown