[Callers] Ideal contra tunes

My teen daughter plays in a performing fiddle group. I sometimes call family dances using the group. The director asked me 1. to suggest some tunes she could teach the group that would be ideal for contras 2. what makes a tune or medley of tunes work well for contras. (There are lots in their repertoire that seems to work for "Southern" squares or big circle dances). Besides being square, 32 bar tunes with A parts distinguishable from B, what makes a great contra tune? I like dancing to medleys where the second tune picks up the energy: how is that accomplished? Can anyone suggest a couple of tunes and (perhaps which recording of it) that are essential to a contra music repertoire? Thanks very much to those who responded to my question about determining space for contra dancing. It was incredibly helpful and I learned something new from each response.