I've been using a laptop as my primary computer for a couple of years now and I use my right hand middle finger on the trackpad and my right hand pointer for the button, the funny thing about it is I'm left handed. Btw it is extremely easy to scroll using this method.
When I do use my trackpad, its usually, right index or middle with thumb for button. When sitting in bed or when using the machine, but not for anything in peticular, its left index/middle and thumb.
left index, left thumb unless i'm feeling special or i'm playing a game, in that case i use my right index finger and right thumb or a totally different mouse to begin with.