When I was building skateparks we had to finish everything by hand and I found the little 8" (I think it was 8") by 3" (I think it was 3") my favourite for getting the most pressure but if I just have to burn a 3" strip or something along the edge for a basement or something then I usually tip the back of the trowel up and put my left hand on the front and give her ****. Thats only if the front is rounded though.