Low Kick deals higher damage to Weavile's most hated enemy Heatran so for that reason I would say Low Kick is better. It also deals good damage to Ferrothorn, getting a 2HKO. It also hurts Terrakion and TTar harder then anyone cares to admit.
Choice Band Terrakion
252 Atk Choice Band Weavile Low Kick (120 BP) vs. 4 HP / 0 Def Terrakion: 406-478 (125.3 - 147.53%) -- guaranteed OHKO
Special Defense Heatran
252 Atk Choice Band Weavile Low Kick (120 BP) vs. 248 HP / 0 Def Heatran: 352-416 (91.42 - 108.05%) -- 50% chance to OHKO
Special Defense Tyranitar
252 Atk Choice Band Weavile Low Kick (120 BP) vs. 252 HP / 0 Def Tyranitar: 684-808 (169.3 - 200%) -- guaranteed OHKO
Standard OU Ferrothorn
252 Atk Choice Band Weavile Low Kick (100 BP) vs. 252 HP / 88+ Def Ferrothorn: 208-246 (59.09 - 69.88%) -- guaranteed 2HKO
As you can see Low Kick gives you a clear OHKO on each of these pokes, with a guarenteed 2HKO on Standard Ferrothorn.