I have recently purchased a few of each, and have been using them frequently. I like how you can change the look of a paper, patterned or not. It gives my projects more depth.
You can see how I used them in a layout i uploaded last week to create the background.
Before I bought mine, I went to this posting on Kristina Werner's blog, to see which colors I liked.
I haven't found a lot of differences between the two brands, I usually get a more even coverage with the October afternoon ones (I really don't know if it's because of the ink itself or the nozzle)-which is not necessarily good-it just depends what look you want for your project.
My one issue with the October Afternoon ones, is that they do not dry completely (air dry, i haven't tried with a heat gun). If you run your finger on it once it's dry you'll still get color on your finger-it's chalky, not wet. But i love their colors.
I have a project on the way with some more ink mists, I will upload it as soon as it's done!
I bought mine at Simon says Stamp and Two Peas in a Bucket.