It all depends on what you use the bike to.. but normally I will say to people around that weight (18 stone/ 114kg) only buy if the rim have minimum a single eyelet and 36holes on the rear rim and 32 on the front (3cross lacing front and rear).
Never be to cheap when buying rims and spokes for mountain biking to dangerous when talking the riders health.
Mavic XM719 would be a fine for 18stone , the Syncros is okay but not more, all depends needs, use and money, XC use not downhill (double eyelets necessarily there).