If you're an elite flyer ex-SFO why would you even care about the UC situation. The Centurion is the de-facto United lounge for me unless I need some customer support. Considering the Centurion is in the UA terminals and not connected to the DL gates, and we're not about to go through security twice—you have to compare the Centurion experience vs. the DL SkyClub experience, and I think T3 wins hands down here.
Also, with CLEAR, security is pretty much a non-issue. Though on the way back the lack of CLEAR at EWR really hurts.