I actually think Calhoun might be the more valuable trade piece. Just because whatever team trades for him will have him for 6 years. With both Trumbo and Bourjos, they will have to deal with arbitration. And you also want to look at it as do you want to really trade a MLB starter, for prospects that might not pan out? Or trade a top end prospect for another top end prospect.
Also, I think longterm, locking up both Trumbo and Bourjos might be a prudent thing for the Angels to do. Trumbo just has so much power, and is still learning. The power is something that just doesn't come around often. Bourjos has potential, but also longterm can be an affordable price.