Honestly, I'd say that the Wrangler Unlimited has been the superior choice for an overland platform versus the Defender for quite a while. The Defender used to have payload and efficiency on it's side in the SWB Wrangler days, but a Wrangler Unlimited can carry as much, matches it for fuel consumption, and is an EXPONENTIALLY nicer place to spend time.
And, honestly, having ridden with a Defender imported to North America on a trail ride, I honestly think the Wrangler is the better off-road platform. Granted, it may have been more down to the driver than the vehicle, but the Wrangler definitely seems nimbler and more stable, the Defender I was watching (A 110 wagon with a mild lift and your normal array of overlander gear) was wallowing around like mad and had to 3-point turns that the Wranglers cruised through no problem.
The Defender is a fantastic vehicle, no doubt about it, but it hasn't had the updates and development the Wrangler has seen in the past decade-it's just outdated, and I don't trust Land Rover to carry on the sheer simplicity of the current one to its replacement.