For me this is between the two most similar players on the list...McLouth and Hart. Both 20/20 guys that are going to be 27 for the 2009 season.
For me, McLouth is the better choice of the two for a couple reasons. First, Hart had a great year in 2007, but fell back a bit in 2008. Was that sophomore slump (technically his 3rd season, but he 2nd with more than 300AB)? It is tough to say. His average took a big hit compared to the .283 he hit in 2006 with 237AB and the .295 he hit in 2007 with 505AB. But he did have a pretty giant BABIP those first two years compared to a very average BABIP in 2008 when he hit .268 with 612AB. Hitters are somewhat able to control their BABIP, but we don't really know how skilled Hart truly is at that. Also Hart's HR rate was down substantially, hitting 4 less HR with over 100 more ABs. He stole 23 bases and was caught 7 times in 2007 and 2008 so that is pretty consistent. Plus he has been merely solid in the R/RBI categories, and I'm not sure there is much evidence that will substantially change in 2009.
McLouth had a pretty nice season in 329AB in 2007 with 13HR and 22SB (1CS) to go with 62R, 38RBI and a .258 avg. Over 600AB that would be 113R, 24HR, 69RBI, 40SB (2CS) and .258 avg. He followed that up with a full season that re-enforced that year, with 113R, 26HR, 94RBI, 23SB (3 CS), and an improved .277 avg despite a 10 point drop in his BABIP. Considering how efficient he is at stealing bases, I could see that total rising in 2009, those the projection systems seem him staying closer to 20SB. So far, he hasn't really given us a reason to doubt him. Will his average ball back to the .265 range? Maybe, but there isn't much reason to think so.
i'm the guy that puts the "nip" in omnipotent...