Regardless of reiatsu and prowess, Ulquiorra would still lose to Baraggan, but I get what you're saying about their being ranked by reiatsu alone not prowess. Still I think Starrk would win. But for years I felt like Ulquiorra would win. For whatever reason my opinion changed more recently. Lol. I think it's Starrk's all around skill. Among the espada his speed was probably the best, in destruction the most impressive after Ulquiorra, he had crazy stamina given the damage he took before going down, and he was probably the most perceptive fighter we've seen in Bleach. Ulquiorra takes it in sheer raw power though and is close in the rest of the stats. Regardless I see it being close and would not be surprised if it really is Ulquiorra who wins.