Is this the official Barnes vs. Collins thread?
Just took a look at 538's projections (not perfect, but convenient):
Collins (categorized as "up-and-comer"): projected 5-year market value of $106.3 M; projected WAR 6.3 this season then hovering around 5 the next few seasons
Barnes (categorized as "average starter"): projected 5-year market value of of $27.2M; projected WAR this season at 4.8, then 2.2, then 1.5, 0.9...
Digging in a little more, I think Collins would improve rebounding at the 4 compared to Barnes and would space the floor just as well. I'm not sure how much you can rely on Barnes' post game when we're talking about him as a 4 compared to as a 3, while Collins has some go-to guy potential, at least in a pinch, shown by his maintaining a high efficiency in past seasons when his usage was closer to mid-20s than this season's sub-20% (as compared to Barnes' inefficient high usage seasons in Dallas). Finally, you simply cannot put age aside when we're talking about a player who is still entering his prime compared to one that is about to turn 30.