Is it better to choose a more-crowded WiFi channel or one with a strong competitor?

You know how many APs are on each of those channels, but you don't know how much traffic each one is sending/receiving (an idle AP doesn't use much airtime), and you don't know what non-802.11 interference might be on those channels.

If the powerful AP is idle, and the less powerful APs on the other channels are really busy, then it would be be better to be on the channel of the powerful AP. But if one or more of those channels is being blown away by Bluetooth, Wiimotes, 2.4GHz cordless phones or baby monitors or other non-802.11 2.4GHz technologies, then those channels would be poor ones to choose and you'd never know from a Wi-Fi scan.

The truth is, you can't figure out the best channel to use based on scans of nearby Wi-Fi networks. You have to test it out yourself.

Put your AP on each channel (1, 6, and 11) in turn, and run iperf between two of your devices while on each channel.

Don't be surprised if your results change at different times of day (neighbor starts wirelessly streaming Netflix in the evenings, or microwaving popcorn, or making a long phone call on the cordless phone, or switching on the baby monitor overnight).