[dsraven]

I find using a wide flexible steel putty knife works well. I have one from doing some drywall work that us quite worn out so really flexible from the handle towards the knife end. Less ridges if worked longer to smooth out and with a steel blade the surface is flatter because less bend across the blade of the knife compared to a plastic applicator. When done scrape the knife off well before the roller dries then sand it clean after it dries. This also wears the knife out a bit more so it becomes more flexible from the handle to the tip of the knife blade which I find helps lay the filler on smooth.