I've come to realise that the best usernames are normally 5-6 letters long.
Short and sweet, easy to remember, easy to spell, not pretentious.
Perfect examples: Cupid. Retro. Kworb. Katie. Matty. Lipton. Conatus. RatedG
2, and so on and so forth.
Some people try a little too hard to stand out with words that are hard to spell and/or hard to pronounce.
Sometimes less is more.