Well, all SARMS stack well together, because they are all safe to use, and there are no side effects that can get a cumulative effect. That depends on your goals, so...
Cardarine GW - fat loss, endurance, faster recovery
SR9009 - the same as Cardarine GW
Ostarine - joint/bone recovery and health, recovery, slightly anabolic
Andarine S4 - pure strength without additional mass
LGD - very anabolic, good for muscle mass and strength
RAD140 - will substantially increase testosterone levels, so it will have similar effects, but a bit milder
Nutrobal - will boost your natural GH production big time.