Tezzeret's ultimate ability allows its controller to draw a card every time they tap an artifact
There are two types of boosters, and each contains a slightly different chance of getting certain cards
Magic: The Gathering Squirrel Deck: Getting Squirrelly in Bloomburrow Limited By Vale Gauthier Hello, wafflers of the internet
So, I think that Rowan is the more powerful twin

1 Wildcard of any rarity A common (18%), uncommon (58%), rare (19%), or mythic rare (2%) card from the Lorwyn Eclipsed main set An uncommon (2%), rare (less than 1%), or mythic rare (less than 1%) fable frame card A rare (1%) or mythic rare (less than 1%) borderless nonland card A borderless reversible shock land (less than 1%) 1 Rare or mythic rare A rare (78.2%) or mythic rare (13.6%) card from the Lorwyn Eclipsed main set A rare (4.6%) or mythic rare (1.2%) fable frame card A rare (less than 1%) or mythic rare (less than 1%) borderless nonland card A borderless reversible shock land (less than 1%) 1 Traditional foil card of any rarity A common (60.4%), uncommon (29.8%), rare (6.5%), or mythic rare (1.1%) card from the Lorwyn Eclipsed main set An uncommon (1%), rare (1%), or mythic rare (less than 1%) fable frame card A rare (less than 1%) or mythic rare (less than 1%) borderless nonland card A borderless reversible shock land (less than 1%) 1 Basic land A non-foil (40%) or traditional foil (10%) default frame basic land A non-foil (40%) or traditional foil (10%) full-art basic land 1 Non-foil helper card or double-sided token Note: Percentages may not sum to 100 due to rounding

Thats especially true because Delighted Halfling can also be tapped for one mana of any colour, as long as that mana is being used to cast a legendary spell