Is it better to loft using extrude or using surface+thicken?
Is the quality of the surface affected?
The difference between these two won't vary greatly. I would use surface + thicken in most cases since it's just easier, plus uses less sketch lines and constraints.
What you use also depends on what the application is. Generally you will get a better surface using the Boundary Surface tool, for the very reason that it allows you to control curvature between surfaces.
I disagree with you here Josh, using surfaces will give you a different result than using solids; because when you thicken a surface it essentially offsets the surface not copy it, it won't show if the thickness is small ...
Please correct me if I'm wrong, I'm still a beginner and always interested in this kind of conversations ...