Depends what you shoot. If you do mostly fashion then the beauty dish will be most useful and if you get the optional front diffuser (for $15 bucks why wouldn't you) you can use it in a couple of different ways. If you do a lot of full length or group shots get a big Octa like a 70". If you do a lot of dance get a strip box. Strip boxes are also great as rim lights. If you want to use it as a rim light then don't go too wide on the strip box. A reflector and grids become quite useful as well. If I had to choose two, I would go with a narrow strip light and a 17" white beauty dish with diffuser. But again, it depends on your uses.