According to Cien, who has knowledge on all the Espada, the 3 strongest things (excluding himself and Aizen) in the Espada were Yammy’s full power Res, Starrk’s wolves, and Barragan’s Respira. So we know Yammy, Starrk, and Barragan all have techniques or forms above Ulquiorra (consistent with Ulq saying 3 people are above him). Whether or not you think Halibel beats SE Ulq is highly debatable, honestly it’s a pretty good in verse debate because I don’t think there’s a clear cut answer, both have good arguments.