Based on what parameters?
Some of those guys are going to be in the majors at lot sooner than others.
Are you looking for their respective value in 2 years, 5 years, 10 years?
Bailey and Dukes are closest to the majors and more projectable, Bailey gets the nod because he's not a douchebag, and because the Reds could be pretty good in a couple years (already pretty young - and have two solid starters, and in addition to Bailey, they'll have Bruce and Votto in the next 3-5 years)
After that, it's about long term potential, and Bruce is far and away outproducing Tabata and Maybin, and even though he's got something like 15 homers, he's got like 35 doubles, so he could easily have 20sh homers at 19, which is in the Andruw Jones / Alex Rodriguez territory.
Tabata is 17, and won't be playing in the majors until about 2010, so it's just waaaay to far away to assigning value to him.
Stewart has had about one full year of productive baseball in his career, and has been really bad outside that. He's not shown power, the ability to hit for average, or very good plate discipline. While the scouts love(d) him, and they obviously know more than I'll ever know, so you can't completely discount him, he's gotta start showing something soon