I think trading Choice makes more sense if they were gonna trade someone right now, unless Dallas is sure Choice is a proven back of Barber calibre. Choice came in at the end of the year when you can argue the defenses were a bit beat down. Next year should hopefully resolve this 3 good backs issue.
I'm basing my opinion off of the tidbits I've gotten from Dallas fans. They seem to think that the front office would like find a way to get rid of Barber.
As far as the defense argument, I disagree. If that were the case, they wouldn't be playing good defense in the playoffs either. These are professional teams that condition for the purpose of playing well late in the season.
Look at the defenses he faced:
Pittsburgh- 88 yards rushing/ 78 receiving
NY Giants- 91/52
Baltimore- 90/25
These were the best run defenses in the NFL last year but for some reason, Choice was able to do what other backs hadn't really done all year. And its not like Pitt's and Baltimore's run D got bad at the end.
Pitt 2 weeks after giving up
166 total yards to Choice ALONE gave up only
85 total to Chris Johnson and LenDale White, one of the best rushing tandems in the AFC last year.
Likewise with Baltimore. The week after Choice gained
115 total against them, Maurice Jones-Drew (widely regarded as one of the best in the NFL) had
88 total yards.
The point is not to say that Choice is as good as those guys (although he very well may be); the point is that he was running well against defenses that were clearly still playing great even at the end of the season.