All these numbers are silly. It depends on how you define "average". In the old days average was distance divided by total elapsed time. (Remember your physics classes? Okay, maybe you didn't take physics.) If you stopped for a snack it still counted as time.

Then someone invented a computer which could do all that for you. Except that it would turn off when you weren't moving, so suddenly the average meant over only the time spent moving. Then someone invented a computer where you could set the speed below which it didn't count. If you cross an intersection at 6mph, it drops your average a lot. If you spend time climbing at 10mph, it drops your average a lot. If you arbitrarily choose not to count those times then your average is meaningless because there is no ideal or theoretically correct cutoff between counted vs. not counted speed.

We often run our tandem on almost-flat sections at steady speeds over 18mph, occasionally breaking 22, 23, even 25 for short spells. We climb much more slowly. We spend a lot of time walking into picnic areas, or slowing or accelerating through intersections. Our computer's average speed almost never breaks 12.4mph. But we spend most of our road time going much faster. So how would you rate our grouping? Surely not A. If it weren't for the stops and the caution I exercise at some intersections it might be B, as long as we don't have to go uphill. But if a group wants to wait for us we can seem to click along pretty well. It isn't quite C though because we have sometimes left casual solo riders in our dust.

The only real answer is:
A - consistently fast, quasi-competitive (despite claims to the contrary).
B - quick, but not a racer's pace, and willing to back it down.
C - casual, not caring how fast you go but enjoying the ride!