The character you have cosplayed that is most similar to you (if none that you have cosplayed, then one that you will cosplay)
I’m not sure I’ll ever have a good answer to this one. Personality-wise, I often pick characters that are more outgoing than me, because part of cosplaying is about getting the chance to let loose a bit. In terms of physical type, I usually end up cosplaying characters that aren’t east Asian, which is more a commentary on US comics than anything else. Although I have thought about making a Lady Shiva (from the DC Universe) costume at some point.