we had an old broadcast bought in '07 with our first boat. used it to teach a TON of noobs until we moved in '13 and board was still in great shape. left it with a buddy that has a boomerang and they still mess around with it today.
have a cwb ride that I bought gf back in '11 and I don't think anyone has rode it in years. the broadcast is, imo, a much better board to train on.
today we use an old p5 danielo pro to teach on.

if you want a surf style boat board as well we had good luck with a koal. durable and pretty easy to teach on.