@anamur-- I used to not want to eat when I took my prenatal vitamins because it left a really strong metallic taste in my mouth. Food didn't taste good because of that and I used to force my self to eat. My doctor switched me to another one after this which has less iron and the taste went away.
He also told me to take my vitamins after I've had my dinner and before I go to bed. Apparently this is the best time to take it because most of us have our stomach the fullest after dinner. Taking it before bed also means that if you get nauseated, it will be while you sleep and it won't affect you much.
So just try doing that and speak your doctor about it if the nausea doesn't go away. I don't think any vitamin is the best, they're just different with some varying ingredients.
One other thing to note is that you should never take aspirin if you take prenatal vitamins with DHA and EPA. Because DHA and EPA is fish oil and fish oil can have a bad interaction with aspirin and could even lead to internal bleeding. Most pregnant women stay away from aspirin, but I just wanted to put it out there.