I haven't tracked down the three circuits yet. That'll be sometime later this month or in August.
Reasons for subpanel:
1) Convenience - disconnect is two floors away otherwise
2) I may not have a space in the basement after everything else gets done (assuming all three circuits are actually in use)
3) Future - I could be in this house the rest of my life. I which case the upstairs gets a remodel needing more circuits.
Although, if I wind up with three spaces, I might just run 3 runs of 12 and let the future tend to itself.