I tried one of these for the first time last week. DH and I were looking at the selection, and he asked the woman working there which one she thought was best. She said she liked the mango, but she said that we could have samples of them to see which one we liked better. We both felt like the strawberry one was way too sweet. This is weird for me, as I have a really sweet tooth, but I didn't really care for the strawberry's artificial sweet taste. We liked the mango flavor, though. It still had a tea flavor to it, but not an over-powering tea flavor.
I don't believe there were seeds in the strawberry, because like a PP wrote, they might not be made with real strawberries. I don't remember noticing seeds. They are slushies, so they are icy and smooth.
Anyway, if you aren't sure which flavor you will like, just ask for a sample of each, and then you can decide.