What is the best non members training area in runescape?

Personal preference plays a part, however i would say hill giants and the blurite cave.

Get a brass key and go just west of the cooking guild. There is a shack by the river. Use your brass key to open it and climb down the ladder. There are level 28 hill giants evrywhere when you head south down there. Head north for hobgoblins (varying levels between 20's and 40's) and Zombies (level 20's). .

then when u get lvl 53 to 55 got to ice giants