I do not think one is better than the other.
Fresh herbs are great to use when they are available. The window for using fresh herbs in tea is very narrow in much of the country. Some herbs such as chamomile are only in their flowering stage for a few weeks in early summer. So during that time drink as much fresh chamomile tea as you want, but once it goes to seed you can start using the dried form.
I make fresh herb teas in the spring and summer as much as possible. I love the vitality and taste of fresh herbs in tea. You feel like you are directly connecting with the energy of the plant. The taste is often more subtle when using fresh herbs and you usually have to use a much larger volume of fresh herbs than when they are dried.
Dried herbs make sense for long-term storage and use. Most of the time I use dried herbs for the teas I make for others and myself. Dried herbs, when the plants have been grown, harvested, and dried well, are nearly as potent as when the herb was fresh. When it comes to formulating herbal teas, most of my blends are formulated for use of dried herbs. Only in the summer section of my book to I have recipes for fresh herb tea. Dried herbs can be used all year round and store well so for tonic blends or teas you want to drink regularly I suggest focusing on dried herbs.