ston
Studio One v3 addresses a lot of the MIDI shortcomings of v2 (although neither Studio One nor Sonar yet has anything like Cubase's Input Transformer and Logical Editor, features which have been in-place since the 80's).  On the flip side, it seems to have joined the ranks of DAWs which appear to be converging towards some future singularity of infinite bundled loops and samples.  Initially, I wasn't all that keen on the new 'cool' interface (prefering v2's), but it's grown on me over time, like litchen perhaps.
 
I switched to Studio One from Sonar because it addressed all of the issues which were frustrating me and preventing me from enjoying Sonar.  Both are excellent programs and represent astounding value for money.  I personally find Studio One to be more stable and robust and prefer the more minimalist interface.  

All good points, same as my findings since using both for a couple of years.
S1 can't hold a candle to Sonar when it comes to MIDI, and I find S1's over emphasis on working with loops annoying.
I do occasionally use S1V3 if I have an audio-only project, and I do like its interface. And it has to be said: I can't recall EVER having a crash in Studio One whereas Sonar crashes for me quite often, two or three times a week (with daily use).  I assume the automatic error reports get reviewed, because I never have any idea what causes the crashes, although it's usually when I'm dragging audio.    

Studio One's midi editing operations are far more extensive than what many Sonar users probably would realise.  Especially now with Note Fx in V3.  I do a lot of midi editing myself and after getting the Groove 3 video on Midi Recording and Editing I was pretty surprised myself as to what I found it can do that I thought was not possible as well.
 
In some areas Studio One is different to Sonar when it comes to midi timing.  Midi timing is rock solid and independent of how hard the audio side of the program is working.  (especially if you can get the midi interface to work over a serial port or the PCI buss. I use a lot of synth hardware through a midi interface as well)  It is also rock solid looping midi and audio over a loop.  Its total gapless performance comes into its own here.  (You can do a ton of stuff while the program is in record or play and it never stops or glitches)  You can also jump midi tracks on the fly while in record and looping over a section.  Something Sonar cannot do either.  (unless that has been fixed in later releases, I am not sure)  I feel the midi timing is one of the best in the business.  I play drums as well as keyboards so I am over sensitive to it.  It was a deal breaker for me.
 
NoteI see Sonar has had some audio and midi engine updates and I would love to check these (midi performance) out again sometime and I will perhaps. I am basing my above observations on previous versions of Sonar so this may be different now.
 
Studio One is not geared toward loop based work either.  It is no different to other DAW's in that regard.  It has just an extensive range of loops available if you feel like using them.  ie You don't have to use them!  It is not just geared to audio only either.  I do massive and extensive midi sequences all the time.  It handles both very well.  It is just geared to whatever you want it to do like any good DAW.
 
It also does provide groove extraction and grooves can be extracted from anything and applied to either midi or audio files.
 
The people who know Studio One very well and are going to give a more accurate perspective are those who use it as their primary DAW, on a daily basis and have for a long time.  If you own Studio One and Sonar and use Sonar a lot I can understand not knowing all Studio One's features.  There are only so many hours in a day!
 
I have never had a crash either since I started using it 5 years ago.
 
The latest version of Sonar looks fabulous as well but I have just invested so much time now into Studio One I am afraid to switch.  I find I can use just one DAW and get the job done.  I do like Mixbus though for stem mixing (sometimes) because of its sound.