I have a 02 RSX-S. I have to say it's a really great car. However, if you really want LSD, get the SI.
The interior of the RSX is also more directed towards the driver. e.g. the instrument panels, radio etc faces towards you. A BIG PLUS!!
The only con about this car would be the alarm system. If you do get a RSX, I recommend getting an aftermarket alarm. These cars are easy to break into. Maybe the SI would be better.
However, if you really want the SI, you should look towards the CSX-S version instead. The minor details are what will really make you decide which is better.