Depends on what you want. I wasn't in the market for an X5 3.5 or a RRS HSE.
I was in the market for a 2012 RRS SC vs. 2012 X5M and I picked the RRS SC. The reason is that I actually go off road. On the road the X5M was it. However, with off-road thrown in it was no contest and I got the RRS SC.
I have had no problems with the RRS SC so far - but it's only been 2 months of ownership. I would say - get the X5 if you are going to stay on roads.