Flax oil sucks. All of it's omega-3 content is short-chain. Your body only uses long-chain omega-3s. Your body can convert short-chain to long-chain, but at only a 1% to 5% efficiency. Take what you think you're getting in omega-3s from flax and figure what 5% of that is. That is what your body is getting.
There has also been some mention about lingans in flax oil acting as phytoestrogens in the body. I don't know about this much though, haven't looked into it. (doesn't matter to me because the omega-3 content sucks anyway)
I like flax powder, but only for it's fiber content and crude protein content.
Fish oil processed from the body of the fish is much better. Fish oil studies are where almost all of the omega-3 information comes from as well.
Health from the Sun makes a great, economical fish oil product that doesn't taste bad. Only runs about $7 a bottle to boot.