As an instructor of all 3 practices, I can say that any are good options for recovery. Many people shy away from Pilates because it is more challenging than some other workouts. Reformer work (Pilates equipment) is probably better for recovery than mat work. Pilates is a nice way to continue to strengthen while getting the stretch at the same time, and you can actually gain more flexibility (elasticity) with Pilates work than with Yoga because of the contracting and lengthening nature of the exercises. (If you are a competitive athlete you might want to consider this as an enhancement to your regular training routine.)
Tai Chi typically is not focusing on stretching, but it is about relaxing the whole body, which also releases tension. Tai Chi is more beneficial for de-stressing and is not as physically challenging as Pilates or yoga.
All these different practices offer different, and yet similar benefits. At the same time, there are several different styles that focus on different aspects of the body, mind, spirit connection--especially when we are talking about Yoga. So, I would do a little research and try a few different things to see what works best for you. Iyengar yoga seems to be all about recovery as well.