Really depends on how quickly you want to get into it. If you can wait for the BJ4 Worlds kit or the Yok, I'd try one of those. I run a BJ4 Worlds and it is MUCH more durable than the XXX4 (I some will disagree).
Parts availability is not a problem with the BJ4, JConcepts ships VERY quickly and I've never had problems getting parts from them.
If I had to buy a new kit that was available now, it would be the Kyosho ZX5