Exactly, it is a matter of taste, personal workflow and needs. To me Reaper is by far my first DAW and later Sonar Artist. Its routing capabilities have no comparison with Sonar Artist, as also its hierarchical tracks system. Also to me Reaper is rock solid in my Windows machine with an incredibly low footprint in my system, something I sadly cannot say about Sonar Artist at least in my configuration.
 
The only thing is that you need to invest a little time understanding Reaper and its philosophy. Once you do that and after a little customization, it is unbeatable. It did such and improvement in my workflow that I did the huge work of migrating all of my Sonar projects to Reaper. Now I use SONAR only for working on projects I share with a friend who only uses SONAR and in order to open old projects.
 
The only thing I miss in Reaper that SONAR have very well implemented is my M-Audio Projectmix control surface driver. Reaper one is a little basic compared with SONAR implementation... but it is something I can live with.
 

My main DAW is Sonar Plat, and I've been using -- and enjoying -- Cakewalk products since Sonar 3 Producer came out.
 
However, I did buy Reaper as a back-up DAW when I was struggling with Sonar Platinum's stability on my previous system. I was using SPLAT with a VS-700 system, and while it sounded great, it was not stable. I went with Reaper not because of any particular feature or workflow element, but simply because it was a very good sounding and sophisticated DAW, that was also really cheap. I don't actually like working in it, but I do acknowledge that it gets the job done, and has a deep feature set. It saw a fair amount of use for a span of about 9 - 10 months, off and on.
 
I have since resolved my SPLAT issues by ditching the VS-700 and moving to RME, and building a brand new audio computer from scratch, with 100% new components. SPLAT is now solid and stable like granite, and I've had no reason at all to fire up Reaper. But its there if I need it, and it never hurts to have a back-up system. 

i started with sony acid (& pro) prob 20 years ago and still use it in certain cases... looping, stretching, pitching.  I have many projects I started on it over the years and still go back and listen to song 'ideas' to resurrect, remix and finish.  I use Reaper for mostly quick ideas or midi building for keyboard midi files... low overhead and quick to get going.  SPLAT is my primary DAW for most projects and final mixes.  Cubase was too klunky and I liked Reason, but the brain cells can only manage so much, so I stopped using it.

If the last time you saw Tracktion was version 2, you're in for a shock. It's grown up a lot.
 
I can think of one good reason for a second DAW: if you have ProTools you can put it up on the screen to show idiot clients who think it's the only DAW for "pros", or who think "ProTools" and "DAW" are synonyms. 

I like Cinnamons.
 
 

I got Studio One mainly for something to use on my Macbook.
I got Mixbuss cause Bapu said it had Mojo..
 
 
 

bapu
I like Cinnamons.

Bun intended.

I use Sonar, but I also have the evaluation version of Reaper.  I put it on to A/B test with.  For example if I run into some issue using Sonar, I like to determine if it's caused by my PC, Sonar, or a plugin.  For example, if a 3rd party plugin works OK in one DAW, but not the other, that's useful info.  Or if it's a audio issue, is it the DAW software, or the audio interface setup, audio settings, etc.?  So having a 2nd DAW can help isolate problems.
 
The only other reason I could see spending time to learn the workflow of a 2nd DAW is if offered something drastically different and useful.  The best example that comes to my mind is Ableton Live.  The session view does something really special.  If you are into loop based song construction it's also very friendly. It's also great if you intend to perform live with a computer.
 
I have an older full version of Ableton, that sadly will not run correctly on Windows 10.  Probably not going to bother paying to upgrade, as I only used it on rare occasions.  Like if I was just looking for a distraction, or just wanted to play around.

For me this comes down to specific functions. I use Adobe Audition a lot as a wave editor launching from SONAR's utility menu, but also master in it a lot. While technically a "DAW," it is more for features non-existent in SONAR, and I feel as a stand-alone DAW Audition is sorely lacking (my version (v4) has no MIDI support whatsoever, but was rebuilt from scratch on the audio side).

abacab
I use Sonar, but I also have the evaluation version of Reaper.  I put it on to A/B test with.  For example if I run into some issue using Sonar, I like to determine if it's caused by my PC, Sonar, or a plugin.  For example, if a 3rd party plugin works OK in one DAW, but not the other, that's useful info.  Or if it's a audio issue, is it the DAW software, or the audio interface setup, audio settings, etc.?  So having a 2nd DAW can help isolate problems. 

 
This is a really good point. I have a software / conflict issue at present  (documented here 
 
http://forum.cakewalk.com/Cursor-movement-over-GUIs-causing-audible-crackling-m3488966.aspx )
 
It would be good info to know if it is present in another DAW. Thanks all for the interesting replies.