I've been keeping a journal for a couple of years now. It's a great way to offload your thoughts and for keeping track of all those memories.
I used Day One for quite some time on iOS and the Mac. It's a lovely app, but has one serious flaw. It eats my journal entries.
It has some really odd and unpredictable sync issues. I've tried using it with iCloud and Dropbox for syncing and they both have serious issues. The last straw was a few weeks back. On the iPad, it had duplicates of about 30 entries. I deleted the duplicates on the iPad. On checking the iPhone, it had deleted the one and only copies of those entries. On re-checking the iPad, it had deleted both versions of the file.
Yes, I could fortunately get them back via Dropbox (thank goodness I was using Dropbox at this stage), but it was enough to make me look at alternatives.
In the time I'd been using Day One, Evernote had improved dramatically on iOS.
I've a bit of a love/hate relationship with Evernote (mostly love), especially prior to about a year ago. The iOS apps in particular were buggy as hell and couldn't be relied upon for anything critical. Well, they couldn't actually be relied on for making notes at all whilst not connected to a solid WiFi signal. That didn't stop it becoming an indispensable app for me (it was still pretty solid for data retrieval), but it did stop me wanting to keep a Journal in it.
The recent improvements to Evernote and the truly useful and utterly fantastic Drafts app, with TextExpander support, now mean I can happily and safely do all of my journalling with a combination of these great apps. You could do it all easily enough directly in Evernote, but I just find Drafts so useful and intuitive that I now automatically reach for it whenever I want to write almost any text, so it's a natural extension for me to also use it for Journal entries.
I use Drafts to get started on an entry for the day, or to add to an existing entry. I've got a bunch of TextExpander snippets I use (to add dates, etc) to make it easier, and then I have some Drafts actions I use to get the notes into Evernote.
If I wish, I can then use the Evernote app to add a nice photo for the day, much as I did with Day One.
I've got another big note in my Journals Notebook which links to all of the day entries in a 7 column grid - basically a clickable calendar table.
Another bonus is that my Journal entries are all encrypted locally in Evernote - a much more secure solution than that offered by Day One.
It all works smoothly and, more importantly, reliably and I'm now happy in the knowledge all of my journal entries are tucked away safe and sound.
If you're looking for a good, cross-platform journalling situation that won't let you down, I can thoroughly recommend Evernote (in conjunction with Drafts if you're using iOS).