TP, with
tWW coming in very close second.
Places chalk full of stuff aren't very indicative of real life. In
TP, you had to really search for the treasure, and the accesses to the hidey holes were varied and interesting.
And don't forget that we have to include snowboarding and the best canoeing/fishing adventures to date into
TP's overworld.
The goodies you found in
TP were more rewarding, especially because most of the treasures were rupees; when you found something else it was even better.
The uncanny valley in
OoT and
MM, in 64 games in general made the games very hard to play, even when the 3d graphics were new and novel, and this was felt more so in Hyrule Field than in other places. The feeling of space and distance just wasn't as effective, and I found that looking into the 'distance' in these games gave me a headache after a while; the blur and lighting effects were just too poor.
Yes,
MM had the deku, goron and zora forms to play with but even with those,
tWW and
TP were better. I find that even playing
TP today, the graphics are surprisingly poor, they were poor at the time and they are even muddier looking by today's standards. In this
tWW has
TP beat, you just can't beat the crisp look of the cell shading in that game.
There was an exhilaration to being free in
tWW, one that was unfortunately relegated until you beat the dark fortress. There just isn't anything comparable to it, that of being your own free agent with a boat you've conscripted yourself, to really and truly searching for buried treasure on desert islands and under the waves. The land you found were valuable pieces of dirt, of value because they were rare and varied and beautiful breakups to the monotony of the waves.
I think
TP took a play from
tWW's play book on this one too, riding a horse is exhilarating in a similar fashion in a certain quality that was missing from
OoT.