REAPER

When I originally chose to use Reaper, it was solely for the low cost of entry. However, after several years of use, and forcing myself to dig in to all it has to offer, I'm really glad it's what I chose. For my use, Reaper is just the best. Here's a few things that I like:

• Routing--the audio and MIDI routing in Reaper somehow manages to be both more flexible and easier to use than any of the competition. There's no such thing as mono/stereo/bus/MIDI tracks. Everything is just a track. Double click and you've got a track that can do any one of those, or even multiple at once if you want. Real-time resampling is also great, so if you're stupid like me and load a 44.1k file into a 48k project it just works.
• Customizability--don't like how the interface looks? Download one of the many user-created skins. Rearrange everything, save multiple screensets. Toolbars can be whatever you need and go wherever you need. Granted, it may take a bit of time to get the interface to where you want, but it's worth it.
• Actions--everything you do in Reaper is an action. There's a log of previous actions as well as a list of every action available. Now, every action can be bound to a shortcut key or toolbar button, or combined into a macro with other actions. I've only scratched the surface myself, but the system is crazy powerful and can enable some super efficient workflows.
• Lightweight and Reliable--loads in seconds, even with large projects that have a lot of plugins loaded. The interface is always super responsive. I've had it crash once on me in the years that I've been using it, and that was from an unstable VST. Obviously the next step would be to instance plugins like Bitwig does so that they can't bring down the program, but I don't believe Reaper does that yet.

Now for downsides:

• MIDI--due to Reaper's straightforward approach, MIDI can actually be pretty confusing to work with until you get used to it. So while Reaper may be more flexible, it doesn't do as much on behalf of the User to make MIDI simple to use. The piano roll is just functional, and it could use a lot of work.
• Included Content--you're not getting the same ecosystem of Instruments and Effects as you would when you buy into Ableton Live or FL Studio. There are included effects (the stock EQ and compressor are very functional), but none of them are super exciting or unique. On the upside, the low cost frees up your budget to shop for third party VSTs.

For certain people, Reaper will just click; other's will bounce right off. Like I said at the beginning, it's perfect for me, and I can't see myself ever needing to switch to another DAW.