Probably one of the most interactive and popular is the 282 gantry crane, as it gives you the most "hands-on" control and therefore arguably the most "fun" of all their postwar operating accessories.
For more automated type of accessories, I'd say the most foolproof that you're looking for (meaning operates with the least amount of mistakes) is the 264 forklift platform, hands down.
The Lionel 3662 milk car & platform, while not as foolproof as the forklift platform, will work fairly well with the unloading of the milk containers versus it shooting them out like a cannon if you set the operating voltage on the control track just right. I would say that holds true for the 3356 horse corral and car you want to replace (again, voltage is key)
Another vote would be the 352 Ice Depot (as stated previously, voltage makes all the difference like the milk car on whether the ice goes in the car or thrown like a football like the milk car).
