Probably SLX. Not as light as XTR but tougher, not as tough as Saint but lighter for the XC stuff. Alot cheaper to raplace than XTR if crashed.

Plus the SLX stuff is updated LX stuff which looks to be on par with the current XT stuff but less$$.
The new SLX rear derailleur is one gram more than a XT for $20 less. The SLX crank looks real nice and is closer in weight to the XT cranks than the LX crank and costs a lot less than the XT.