I'm a big fan of flash fiction. It's ideal when you only have a couple of minutes to spare, say while queueing at the supermarket check-out. As for the writing of micro fiction, it's great for a quick boost of confidence in your writing ability because you can finish several short short stories in an hour.
The competition I've chosen today is for the next themed edition of Short, Fast and Deadly: Sgt. Pepper's Lonely Words Club. Stories submitted for the issue must make use of a corrupted or re-contextualized Beatles Lyric. I've written several just now and had a blast. Now I'll sleep on them and in the morning I'll see which of them are any good.