Well technically 1/8" is better (bigger) by about 0.007" (sorry, 0.375mm!) ðŸ¤
Of course graphite would be preferable to lead but it just doesn't have that same metallic "twang" when chewing on it.
All my drafting pencils are 2mm which I really like for shop work since the lead doesn't break constantly when marking up a board. 3mm would be even better!