This is an interesting piece by Howard Megdal on outfield defense in left and right field (HT: Rob Neyer) for the New Yorks Mets, and one that may also be applicable to the Orioles. Nick Markakis has a reputation among fans and the media as being excellent defensively, but I suspect most scouts (and certainly the defensive numbers) would say he has perhaps average range and a very good arm. Felix Pie may be the opposite in left field, while Luke Scott is a bit below average on both counts.
Neyer notes that if more balls are hit to left field than to right field (a right handed batter pull bias) then it stands to reason that left field defense would be more important than right field defense. That may well be true, but I'll suggest one more reason: left field is inherently more difficult than right field. In my experience, it is much easier to pick up the flight of a ball hit by a right handed hitter in right field than it is in left field (reverse that for left handed batters). With more right handed batters than left handers, this difference does suggest that the outfielder capable of getting better reads should play left field.
There are, of course, a few other issues that we might consider:
1) Who has a stronger arm? This is certainly important; throwing is more important in right field than in left.
2) Are there any ballpark specific factors that affect the decision? For instance, right field in Camden Yards, with its high wall, grounds crew viewing zone, and tricky corner, may be more difficult than left field.
3) How do the day's starting pitcher and opposing line-up project batted balls? Perhaps with left-hander on the mound against a right-handed heavy line-up a manager should place more emphasis on left field defense.
If Nick Markakis is one of your two corner outfielders, then it certainly makes sense to play him in right field; his arm is his most valuable defensive attribute. If, however, you're going to give Nick a day off and are trying to decide which corner should by manned by Luke Scott and which by Felix Pie, perhaps the counterintuitive but correct response would be to play Scott in right. Anyone have some data?