What is the best member thing to train deffence on in runescape

It doesn't really matter much what you train; the amount of experience depends on the damage you deal. Just don't fight monsters that are too powerful (costs you too much food). It is convenient to go to monsters that are more than half your combat level, since monsters below that level are usually not aggressive (they don't attack you automatically). Also consider the combat triangle; for example, if you prefer to attack with magic, you have an advantage against creatures that attack with melee.