Good brands of Omega 3 vitamins?

I'm looking to get at LEAST 600mg DHA a day, and also EPA. I am looking at products online and am just completely overwhelmed at how many brands there are. I see that Nordic Naturals is supposed to be a high quality brand, but I wonder if it really makes that much of a difference? I'm checking out Kirkland's too, as they are cheaper, but they appear to contain a lot of preservatives/unnatural ingredients. Anyone know of any good quality vitamins at a good price? I'm looking at amazon and ebay. I wish Dr. Oz listed which brands were good, I'd buy them in a heartbeat.