yeah mihawk is awesome cause he got his powers by himself, not by a DF like everyone else (except jinbei and partly hancock). hes a real swordman and hes cool.
for donflamingo, i think he really has the most mysterious aura around him. but that only comes because we havent seen much of him until now. if we get to see more, the aura will fade away and we will see that he is not the great. if i remember corrctly, he had the highest bounty out of the shichibukai (something like 350.000). so we can expect something from that guy.
btw. does anyone happen to know the bountys of the yonkou? would be really interested at witch bounty they stopped counting . . . :P