A weak El nino is characterized by a trough in the Eastern US and a ridge in parts of the Western US. On the right, in the GFS, we see a deep trough in the East Coast, as well as a ridge pushing into the Southwest and Plains. This is very typical of an El Nino, and I do not dispute that the atmosphere is indicating that the El Nino is beginning to take hold.
On the left side, we see the ECMWF. It has a major ridge of high pressure in eastern Canada, with what appears to be a trough pattern in the Southeast. However, note the depression of height anomalies in the Northwest. This is not a sign of an El Nino- a ridge should be in that area.
In this case, I would trust the GFS more. Notice how both models have a ridge near Greenland, known as a negative NAO. Both have the ridge on the western side of the land mass. A negative NAO will typically consist of a stormy pattern in the East, like what the GFS is showing. That said, the GFS appears to have a more reasonable scenario, and that is one I would like to believe at the moment.