Bit late to this thread, but here's my $0.02 anyway...
I think Gerard's textures look nicer - they'd be more compelling to people who've never played WZ to give it a try.
However, during gameplay whatever conveys the terrain best is better. Eg. I saw the post regarding cliffs that don't look like cliffs and navigable land that doesn't look navigable.
So I'd probably plump for something mid way between Gerard and MaNGusT.
My only fear is that making the game look nicer delays fixes to the VTOL bugs. Also, if the terrain textures are improved, will units/buildings start to look ugly and thus they too will need updating?
EDIT: MaNGusT's textures do look more realistic though - I think what threw me is that the current building textures look a bit pants. If building textures were updated (maybe also with semi-transparent foundations) MaNGusT's textures would probably be a clear winner.
Some of the best textures I've seen are those in the game Stronghold 2 by Firefly Studios. That game also had a rather good map editor which I spend many a happy hour in making very tasty maps. In particular they had some spectacular water effects (waves, waterfalls, etc) and the ability to add sound effects to the map (eg. birds chirping in a forest, wind howling near cliffs, etc).