I assume your B1/B2 visa is currently valid? If so, just fill out an I-94 and enter on that visa. The I-94 does not ask about previously denied visas, just info on your current visa. The I-94W (visa waiver) is the one with all the questions. You were asked all those questions when you got the B1/B2, so they don't ask again.

You should not rely on the visa waiver if you've ever been denied a visa. Just use your visa.