I have not used any other software but I have gone through demos of others and LogDNA gave us everything we needed at a fair price and with a great UI on the back end. It was not even a question of which software to choose. They are a great team.
LogDNA was already setup when I started and it is offered through Heroku so that's why it was chosen. It's also cheaper I believe. Compared to Logentries, it does the same thing.