No one can tell you who to cosplay. It'll be a better job and funner project if you ask yourself these questions before deciding:
-What characters do you like from that series?
-Can you make/buy/alter the clothes needed for that character?
-Are you willing to spend the needed time making/altering the clothes for that character?
-If you do not look like that character but still like that one, would you be willing to get the needed hair style/wig/hair coloring/make-up to match skin tone/sex change?
Trust me, I know what I'm doing.
Erm...if you know what day in advance you do an X/1999 cosplay, I could meet up with you. I'm going as Arashi Kishu on Sunday...at least...I'm pretty sure. Since Friday and Saturday are planned for x.x;
Good luck in whatever costume you choose, in any case!