I'd go with the ore elemental chests. I had a near complete collection of demon names on Catskills (Used to roleplay a Holy Mage/Demonologist) and IIRC, was only missing five or six of the names.
I also spent a ton of time running around with my RL friend. I had been pushing him to buy UO for several months and he finally did. His first character was a crafter. First GM skill was mining. So I bought him a buttload of gargoyle pickaxes and would follow him in Ilshenar killing any elementals that spawned.
God knows how many hours and pickaxes we burned through, but after doing this a few hours, three or more times a week, for about four months...
All I got was one damn verite elemental paragon chest.
You have to figure its what? 1%? to dig an elemental with a gargy axe?
Then 5% for the elemental to be a paragon? THEN 10%? for that paragon to drop a chest?
.00005 to get one. On average, you would get five chests for every 100,000 blows of the ole gargy pick... No guarantee that those five will be unique either, so good luck completing a set!
Disclaimer: My degrees are in Music, not Mathematics. If any of you math types see a flaw in my calculations, please feel free to point and laugh. Then please post the real odds.