After about a year of trolling SL with a newbie skin and shape, I decided to get serious and invest in a quality av that had many of the same physical characteristics as me, but with the ability to be customizable. So, as far as skin, shape, clothing and accessories, my av strongly resembles me in RL. The only changes I make is the different hair styles and colors.
My thought process was to create an av that I could identify myself with and be happy about, especially if I was going to be investing L$ on it. Turns out that the av I ended up creating strongly resembles me and how I see myself, so it's really an extension of who I am in RL.
Good luck on your research!