For the most part I get crap like a Pine Scepter or some such other useless dreck.
Any dwarf without a "moodable skill" (and Craftdwarves and Engravers, etc.) will produce a random "craft" trinket (aka "dreck"). This is most common on farmers and such.
If you want to avoid that, take any and every migrant without a moodable skill, and have them produce 1 weapon, piece of armour or some such (depending on Preferences), and then don't let them do anything that would over-ride that with another moodable skill.
(Most easily done by manipulating labors via Dwarf Therapist and/or workshop Profiles.)
You can even over-ride undesirable existing skills (such as Engraver or a Craft, etc.) farily easily by simply letting them toil at some preferable profession, like Miner or Mason (making stone blocks).
http://dwarffortresswiki.org/index.php/DF2014:Strange_mood#Skills_and_workshopsAs for my best? I rarely get drek, and often get obscure weapons - some less useful than others, but when a mood strikes a weaponsmith, I'll shut down the entire fortress if I have to*, [f]orbidding all metals except Steel, so they have no choice except to do it right, tyvm.
(* In a mature fortress, my goal would be to have all my forges lock-able, all ready and waiting with a small stockpile of desirable bars in them (steel, silver, etc.), ready for any moody dwarf. It's only the 1st bar that determines the metal, the rest are decoration.)Beyond that, artifact mechanisms in weapon traps are nifty, as are furniture for noble rooms, but nothing jumps to mind atm.