IEEE has a proven history of being more supportive to open standards than 3GPP although a lot of efforts have been made towards open standards in 3GPP.
The main difference between WiMAX and LTE is the deployment strategy.
WiMAX requires a new network to be built whereas LTE is an evolution of existing Wideband-CDMA/High Speed Packet Access (HSPA) networks and therefore it has the footprint advantage of close to 80% subscribers worldwide.
With UMB (Ultra Mobile Broadband) no longer an option, both CDMA and GSM operators are heading towards LTE.