I love Lines for the nerdiness. I like the option of making your own custom plan, and then being able to check off attractions and have it update the absolute best way to do your remaining attractions based on real-time info. I love having it on my phone...I'm home in cold Ohio, but sometimes to pass the time I check to see how long I'd have to wait if I wanted to ride TSM right now!
I used to like the Disney app too, only for dining reservations. I didn't find its wait time estimates to be as accurate as Lines, but I loved being able to click and button and find restaurants near me with availability, and make the ADR with one more click. I make ADRs in advance, but as we all know, life and lines can get in the way. The Disney app made it a breeze to adapt on the fly. But I have to say I used to like it -- I got a new phone, and the Disney app is not compatible. Same carrier as I had previously, so I assumed it'd work, but apparently not.
I also love the transportation wiz -- click on where in the world you are, and where you want to go, and it tells you all the Disney transportation options, and estimated travel time for each. It's from My Laughing Place, T-Wiz.