Sammael
Adventurer
Because, from my experience, the vast majority of D&D players can't deal with that. When placed in a sandbox, those players are simply overwhelmed with the idea that they can go anywhere, do anything... so they basically waste session upon session on pointless bickering regarding their party's direction and goals. If they even manage to form a party in the first place (since forcing the characters to start as a party sort of defeats the point of the sandbox).What I've never understood is why so many D&D games don't begin with the same premise. From the adventurers' perspective, you've got armor, weapons, maybe a spell book, and some gear, and a handful of coins in your purse if you're lucky. On the most basic level, what happens when those coins run out?
I've only met three or four players over my 12 years in the hobby that could handle sandboxing well, and I've met a grand total of one game master (who runs Warhammer Fantasy as his game of choice... it's an easy setting to sandbox).