i like the back alley too for a few good reasons:
1. only 2 entry points - the alley itself in front, and the back window
2. if everybody is outside at the start of the round, you don't get the gassers
3. when you do get overrun, you have the back door to open to make a get away
4. you can plant 100 trip mines for your back up plan.
An alternative to play the alley is like this (but you need mics and teamwork):
1 player at the back window
2 players stand at the fence by the little AK74 on the wall.
1 player stands in the middle (by the garbage can) to protect the 2 players by the fence from the zombies falling from the roof.
I like this strat because the 2 main big gun shooters have a straighter line of site and get more kills per bullet and don't run out of amo so much. You also don't get over run as much as when 3 players stand back by the garbage can (the zombies falling from the roof really screw up your line of site and cause a bit of chaos.
