Safflower is a much better source of CLA. If you take 1 gram of Sunflower Oil, only about 40% of it will contain active CLA. So, in 1 gram (1,000 mg) of Sunflower oil CLA supplements, you only get 400 mg of CLA.
Safflower oil contains 80% CLA. So, in 1 gram (1,000 mg) of Safflower oil CLA supplements, you get 800 mg of CLA. Unfortunately, because Sunflower oil is much cheaper than Safflower oil - most companies will try to use Sunflower Oil CLA in their supplements.
As far as whether you should take CLA or Safflower Oil, this article about a recent study came to mind.
The researchers behind these data are applauded and honored for their efforts ? they have generated a hypothesis that can (and should) be tested. That is not the same, however, as saying the results imply that anyone interested in losing abdominal fat should begin taking a safflower oil supplement.
I suppose it's up to your interpretation whether taking Safflower oil is more or less effective then CLA. I've used this in the past, Orbit Nutrition - Buy Primaforce Max CLA For Cheap!, but I'm afraid I don't know whether this is a vegan CLA or not. Ultramarathons are pretty hardcore.
In the study, the effects of taking conjugated linoleic acid (CLA, an agent promoted for weight loss) and safflower oil over two 16-week periods were compared. By trial?s end, the researchers found that subjects taking safflower oil experienced a significant loss of abdominal fat compared with those using CLA. Problems with the study begin with the small number of participants (55) and the number who dropped out (20). All the people involved were postmenopausal women with type II diabetes, begging the question of what the effects might be in men or younger women. Adverse effects occurred but were not specified. In addition, safflower oil was compared to CLA, an agent that has been reported to increase insulin resistance ? the comparison may thus not be fair from the get-go.