IMO, the single-ride $15 (minus passholder discount) is the way to go. That way, you know you'll get to ride everything once with no wait. If the line is short, you can hold it until later in case the lines get bigger. You get 9 rides for the price, so that's (approx) $1.50 per ride. If there's an hour wait at the Griffon on someone said "psst, I'll let you skip the line for $1.50" you'd take that wouldn't you? That's how I look at it anyway. I think the $40 one is overpriced and usually unnecessary.