I've had the Sparco spline type unit but found although good due to very little slop, it was also often a pain to re-attach the wheel in a hurry due to they run a neccesary master spline (especially if you've not left the steering dead straight), as you sometimes need to when running from the little girl's room to the start. They're also too expensive.
For 18 months I've been using the D1 Spec from JJR, http://justjap.com/store/product.php?produ...at=0&page=1, and to be honest, can't really fault it, no slop, quick to release and engage, easy to line up when engaging, and cheap as chips.