I'd prefer the thread be Old Barnwell & The Tree Farm rather than versus, because what's worth celebrating is how different the two courses are from one another despite their proximity and similar opening years. Tree Farm possesses a calming sense of intimacy and isolation on its property. You feel the presence of the surrounding woods more acutely, the land never lacks in scale, and I've noted elsewhere my fondness for the restraint particularly in the front nine and the surprising number of green sites without bunkers. My favorite hole is the 5th, even though I didn't have to deal with the Kyebrows!
Old Barnwell is brawny, almost unnervingly open off the tee, because you feel like you're going to get baited into a wrong line, and the clarity of the question reveals itself the closer you get to the green (or in my case, as I was walking off it). I felt like Old Barnwell had me thinking about where I was trying to put my ball more than most American courses I've seen. But maybe I'm already damaged goods in this regard because I've gone with driver down to 7iron off the tee at Ballyneal's 12th--and still have little assurance of what's the best way to handle that hole!
I had 36 hole days at both courses on back to back days last February. My scores were nearly identical across all four rounds oddly. The difference in how those strokes accumulated was from screwing up a few drives at TF but putting better on those greens, whereas I was always in play at OB but then screwing things up closer to the hole. I wouldn't consider Old Barnwell harder, nor a harder walk, but more intellectually demanding.
When I fly across the country to visit Aiken again, I'll be disappointed if I miss either of these courses. The variety between them, and their mutual high-quality, results in a special combination for members and guests who have friends at each. I think Tom is one point too low on the Doak scale for one of the courses. I know I'm keeping my opinions in the middle, but I adore both, and look forward to seeing how the clubs continue to express their own characters now that lodging is completed at Tree Farm and getting closer at OB.
And while we're at it, Broomsedge also appears to have differentiated itself from both Tree Farm and Old Barnwell. Amazing that the region can lend itself to such an array of architectural and aesthetic variety.