I'm a weak weightlifter, my cousins an international gymnast. We went to his gym together and I could lift at least 40kg more than him on the main lifts (squat, bench, dead). With dips and chinups he beat me - but I was still strong enough to do a few of each. His coach told me that most of gymnastics is technique - brute force doesn't make world champions.
So, from my first hand experience I;d say weightlifters are stronger. Taking strength as 'the most lifted' rather than 'the most times lifted'.