Over the last three seasons, Lopez hit .280/.351/.392, while Bartlett managed .288/.349/.403. Bartlett did his damage in a tougher hitting environment, but those lines are still closer than they are distant. Lopez walked a lick more (9.6% to 7.6%) while Bartlett fanned less (15.1% to 15.9%) and hit for a tick more power (28% of his hits went for extra bases versus 27% for Lopez).
Bartlett appears to be the better base runner, taking the extra base 45% of the time (with a 76% stolen base success rate) whereas Lopez takes the extra base 33% of the time (and succeeds in steal attempts 58% of the time). Lopez is also worse at fielding, although he is playable at second and third base and ostensibly, a more troublesome attitude, meaning Bartlett is the better player overall.
Those differences are part of the reason Bartlett’s contract ensures at least double of Lopez’s 2011 salary, and that difference is part of the reason Lopez and not Bartlett will (probably) be on the Rays’ bench.