North Terminal is much nicer in my opinion. South is where the railway station is so that is good for EZY but I would have thought that is less of an importance to TCX and ZB since they only have leisure passengers who are much less likely to travel by rail or need to commute into central London.
I don't think it would take much to get TCX and ZB to move North along with Thomson (why did they move by the way?) Perhaps VS should go North anyway along with the majority of long haul traffic at Gatwick. I can definitely see EZY at just one terminal in the future, it certainly brings no benefit by splitting services between both!