I'd stick with Santana. K/9 is always a good guide.
And Pineiro was in long relief only a couple of seasons ago before he made the transition to starting. So both Santana and Pineiro are former relievers who are now starting. Of course, lots of teams do this with young talent. They bring them up to face ML hitting in a relief role before moving into the starting lineup. Strikes me as a wise idea ...
Or was the claim being made that Santana is better suited to long relief? If so, I totally disagree.
"The game has a cleanness. If you do a good job, the numbers say so. You don't have to ask anyone or play politics. You don't have to wait for the reviews." - Sandy Koufax