Difference between the output method

Hi, 

I wanna ask the different betweent these two lines in the output of the model,

    model = Dense(2, activation='softmax')(BP_hidden)
    # model = Dense(1, activation='tanh')(BP_hidden)

Is there lots of improvement when choosing the first option?
Besides, is there any probability to choose sigmoid activation in place of the second line's tanh?

Thanks!