I actually use a small tweak: rather than "all are equally good so I'm choosing based on salary," I pick the company I want, then go to the others and say "another company has offered me X. Could you offer me a little more?" Once they do, I go back to the company I want and say "another company has offered me Y. I really want to work for you, so could you match Y?" Perhaps the "I really want to you," and only asking to match another offer, is more important than I thought?