I'm using Ulysses. Also a rental app, but I think it brings a lot to the table if you have a lot of other work to use it for. I toyed with using Agenda for this purpose but all my other writing is in Ulysses so I put it there. To be honest, I could just as easily create a Pages document, put each entry on a new page and call it a day (or, a succession of days).
Indeed. The only reason I am using Day One right now is that I got it last year for USD 25, which I believe is fair price for it. In the next few months, if I do not get it at that price, I will have to think it over.
I use Ulysses for my professional work, so I tend to keep it separate from any other things. I do not want to have an unwieldy library that I might lose thread of on occasion, inadvertently mixing professional and personal content.