Well the scariest was probably the riptide, because it did most of the killing. I just killed other stuff because if I didn't it would have done more damage than the Riptide. I always kill scoring units first, period. If they can't score, they can't win. If you take out all the vehicles, generally Tau don't do all to well. The pathfinders need to die fast, especially when you're playing Deldar against them. Marker lights will ruin you every time. I'd say that the Razorwing did well, but only because I got rid of Shadowsun's unit with Skyfire and Interceptor. And I'd probably take another one, but Ravagers are better against Tau if you put flickerfields on them because they just have better AT than the Razorwing. Plus Tau can get stupid amounts of Skyfire. Usually, at least with my playstyle, I have enough AI without the Razorwing. It really depends on your style of fighting.
Hope that helps :)feel free to message me with any other questions of any kind!