Stating the obvious but as you know, freestyle pro scootering is a high risk sport. The tricks that you see the professionals do are practiced over and over. And even they miss every once in a while! While there's no equipment that will protect you 100%, there are must haves. Last post was about scooter helmets, which should be a requirement.
Make sure that these pads fit snug, with minimal impact on restricting movement. The outer shell should be durable and hard enough to withstand some punishment. Inside of the shell should be padded and comfortable.
There are a lot of options out there, but the most important thing is to wear them when you get them. They don't protect anything on the floor in the garage.