Passion flower, valerian root or kava which is best for anxiety with less side effects?

No single best. Just like there is no best single drug for anxiety, there is no single best herb. We are all unique biochemically and a drug or herb that might work great for one person may not help another at all. Of the 3 you mention kava causes the most side effects. You can try passion flower ; valerian to see which works better for you, but holy basil (tulsi), rhodiola and l-theanine are also worth trying.