Getting around mana costs is a powerful ability
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

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

So, I think that Rowan is the more powerful twin
This might be due to the precon curse of fairly random cards like Glint Raker and Audacious Reshapers that slip into the deck