FlagRSP2 and MyRolePlay both give you a space to write things like your character's first or last names, a character title (such as "Priestess of the Dark" or "Wacky Troublemaker"), as well as some description about what your character looks like; and of course they both enable you to see the information other people have written about their characters too. Both have "roleplaying flags," which can tell other people whether you are a "casual" or "fulltime" roleplayer, as well as whether you are in or out of character at any given moment.
FlagRSP2 has a cleaner, more intuitive interface, in my opinion, and it has nice little popup windows for character information which can appear whenever you mouseover or target someone. MyRolePlay only has a popup button which you must click on to see other characters' information, but it also has two separate spaces for physical descriptions and story backgrounds, which FlagRSP2 users sometimes mix up together. MyRolePlay also uses less computer resources on my system, and keeps things running a bit smoother. I often switch between the two since I can't really decide which is best.