Conflux is a rush castle. Build up Phoenixes and go for it.
Tower is a slow-paced castle. But if you develop it, it becomes incredibly strong: mages and titans attack, genies cast spells, and nagas strike.
The key is that stronger units in small numbers are not dangerous. Weaker units will defeat them due to their numbers. As the numbers grow, the strong unit "catches up" to the weaker one.