Having driven both MDX and RX 330, I can offer my views.
If you are passive driver who drives a car gently and is not in a rush than RX 330 is for you. The transmission does have a lag but you wont see it if you drive defensively. The vehicle in fact forces you into defensive driving habits. Additionally, the vehicle is refined with less road noise and the ride is much smoother on rough terrain than the MDX. The interior of the Lexus also feels much superior, and there is less lean at curves than the MDX.
On the other hand if you are an aggressive driver who drives vehicle hard, is used to making split second decisions when merging into traffic or during changing lanes in heavy traffic, MDX will serve you better and RX330 will probably get you in an accident. MDX has absolutely no transmission lag and very responsive. The interior is also much larger than the RX330. Engine noise, acceleration and general handling is probably comparable in the two vehicles.
Hope this helps.
