Txtlit seemed a good, low-commitment comp to go for, since it requires a maximum of 154 characters and you enter by mobile phone. I am by nature a concise writer (except when writing LJ posts, apparently), and keen on getting the right word in the right place, so the format suits me very well.
Although there's no fabulous cash prize for any except the top entry, I was gratified to have my very first attempt shortlisted.