"one of the reasons people say they prefer the double over triple is that it shifts so much better."

Not true for me. On a typical triple, it's fairly easy to stay in the middle ring most of the time. Cross-chaining? It's not an issue.

On the other hand, switching from the big ring to the little ring, or the reverse, on a compact, means moving up and down about four cogs in the back to reach the next nearest gear. On the triple, its about three jumps.

So, for me, on a triple, it's less changes of chainrings, no cross chaining, and less jumping around on the back.

Each kind of bike has it's purpose, though, so in the end, none of this matters.