chin-ups - military or standard grip??

chin-ups - military or standard grip??

with chin-ups (close grip pull ups) what are the advantages/disadvantages to the two different grips?
my gym has a pull up bar that has extra handles sticking out at you near the middle of the bar (for military grip I think?)
anyway, with that grip your palms are facing eachother instead of toward you.
Just to illustrate, I'll try and describe the extra handles better...
If you were to look at the bar from straight below it would look like this:


___I_I___

When I do pullups, I mix it up. hands side by side, 6 inches apart, shoulder width, as wide as the bar is, shoulder width behind the head, wide behind the head, chin ups, side by side, shoulder width, and wide. Sometimes I take the bar from the pulldown machine, the small triangular one and throw it over the pull-up bar and do them side to side.