The best chests in borderlands 1 are in order of containing the most loot:
1 Crimson Lance Chest (requires The Secret Armory of General Knoxx).
2 Red Chest
3 White Chest
4 Ammunition Chest
In the base game they are color coded, red chests contain the most guns, then white chests.
But if it is the best loot (pearlescent items) you are after, the best guns drops are listed in this table. They basically only drop from high level monsters, including Crawmerax the Invincible. These all require the The Secret Armory of General Knoxx.
For more information on the best items without this dlc, look here. On first play-through there is a special hidden red chest that has reputed higher chances of having good loot. The Hidden Developer Chest
I could not find lists of chest levels, so I don't know what determines the drop level of items from chests. I don't know if this means that there are no best locations to get items from chests. Or if they all just scale to your level.
New Haven It is lootalicious
If you want to 'cheat', you can abuse the patch mechanics to get more loot quicker from new haven. First do not patch the game up to 1.3. This means that new haven still contains 7 chests (2 of which are red chests). After the patch all the red chests are made white. If you also only do loot runs while the quest: "Another Piece Of The Puzzle" is active, you can access two more chests in new haven, for a total of 9 chests. The wiki has a map
According to one of the loading messages "More players, stronger enemies. Stronger enemies, better loot". I have no idea how that is supposed to work. And if it results in better stuff from chests.