I'd love to go with the smaller tractor if possible because it would fit better with my current equipment, but I'm not sure it's large enough for everything we need it to do.
With that in mind and the fact that you have 3 other tractors already, I'd lean towards the larger 4wd units to handle those unknown chores. You could afford to leave them hooked up with implements. That would be icing on the cake (IMO) giving you the ability to tackle whatever comes up?