Orb Research
These are the test results for what is dropped by hitting an enemy orb for items when it is a specific colour. The most useful orb to get refills from is the purple orb, and the least is either green or yellow.
Notes:
Bombs and arrows are interchangeable
Darknut (in front of entrance to Ganon's Tower)
Green orb spoils- 2 green rupees, 1 blue rupee, 2 arrows, 1 bomb, a knight's crest.
Orange orb spoils- 3 green rupees, 1 blue rupee, 1 arrow, 1 bomb and 1 knight's crest
Purple orb spoils- 3 green rupees, 1 blue rupee, 1 knight's crest, 2 arrows, 1 bomb
Moblin
Green orb spoils- 4 rupees, 1 yellow rupee, 1 arrow, 1 skull necklace
Orange orb spoils- 2 green rupees, 1 yellow rupee, 1 arrow and 1 skull necklace
Purple orb spoils- 4 green rupees, 1 bomb, 1 yellow rupee, 1 skull necklace
Keese
Green orb- three green rupees, full pot of magic, half pot of magic, arrows
Amount of times you can steal from an enemy with a grappling hook:
None- Keese, rats, bombchus, killer vines
1 steal- Peahat, Chuchus
3 steals- Bokoblin
4 steals- Moblin
5 steals- Darknut
Note 2: It seems that the tougher enemies always drop an item orb, while weaker ones often drop simply a basic refill of something or money.