Hi fakepig, I agree with others that a good KG is more important than the am/pm schedule. The "生理時鐘" of taking afternoon nap is actually what YOU arranged for your kid and can be changed and trained up.
My 1st choice offers pm class and my daughter has to go by school bus. Another KG which is very near my home offers am class. But I choose the pm class as I think I can adjust her schedule and the learning environment is very important.
Then I will try to change to am class for K1 if possible.
many has said am is better for kids' learning. on 2nd thought, pm is also good, at least no need to wake up early, and it is also tough in winter for both kids and parents. Just 3 hr in PM, should be fine to the kid.