The Leslie street spit is best if you bike it or have rollerblades, or if you like to jog. Otherwise its a pretty long walk to get anywhere. On the plus side they are making more walkpaths close to the shoreline so you don't have to walk too far in to enjoy the view. But if you do go in more you can get spectacular views of the Toronto skyline.
For Cherry beach, its pretty small in size and pretty quiet in comparison to Woodbine beach. So if you want to enjoy the beach without too many people around, Cherry beach is a good place to be and it has nice views too.