We loved the Maid of the Mist (with the observation tower) and the Cave of the Winds! The bus is a great way to navigate the American side and not have to fight for parking; however, Whirlpool State Park is underwhelming and the delicatessen is great, but not worth the rushed experience at the Cave of the Winds and Maid of the Mist.
If we had to do it again, we would have just booked the Maid of the Mist and the Cave of the Winds, and spent our time exploring both areas more. Also, I recommend waiting until midday for the Maid of the Mist for a clearer view of the falls without the sun behind them.