I sometimes think having only one journal would be ideal, but that's not likely to happen. I know me, and I'll never stick with just one.
Currently, my primary (non-paper) journals are kept in Day One and Org Mode.
Day One is a pleasure to use. It looks great and makes journaling quick and easy on every platform I use. It automatically adds location and weather data to each entry, which is a nice bonus. The printed books from Day One are also great.
In Org Mode I use org-journal. I like writing in Emacs/Org-mode and I like plain text and I like Org-mode's flexible export options. Basically, for writing things down, I generally prefer to do it in Org-mode.
I'm trying to level the playing field between Day One and Org Mode. To this end, I've added a couple of tweaks to my org-journal.
First, I've made it easier to drag and drop images into entries. To do this, I used a bit of code from John Kitchin. Still not as easy as Day One, but better than it was.
Next, I added a quick way to insert the current weather conditions into an entry. This is done using wu, a command-line interface to Weather Underground. Wrap the command in a SRC block and org-babel renders the results right in the entry.
I just put the cursor on the BEGIN_SRC line and hit CTRL-C CTRL-C. Neat.
I could probably find a good way to have the SRC block automatically created with new entries, but for now, I just use a TextExpander snippet. Close enough.
Here's what today's entry looks like so far. Not bad.