FWIW, I've used SOnar since V2 in what is best described as enthusiastic amateur looking to doing more with the right premises. i.e. I do work and record others but not as often as I'd like.
I use it for around 30 hours a week so I'm not taxing it a great deal but some of those 30 hours will be a 12 hour session. I don't use a huge amount of soft synths, it's mainly hardware synths for my MIDI stuff. Typical project 10 - 20 MIDI tracks, 20 - 30 Audio, 15 - 20 busses and around 30 - 40 plugins as well as using the PC EQ compression on most channels
Bugs aside and apart from last week when I had issues caused by memory timings on my O/C profile (which was crashing everything not just X1) I've found X1 rock solid, and I mean rock, since release. I've had maybe 2 or 3 crashes since release caused when I was testing a buss envelope cut & paste bug and once when I set a screenset to a snap value of 0 ticks, apart from that nothing in the stop or crash dept.
I find it better than other versions for looping. Only time I get loop dropouts now is if I try and move either the whole loop, or the start/end times outside of the now time. In a comping session I'll be looping, moving, changing etc for anything up to 2 hours without a break & without it dropping out. I've never been able to do that before.
Anyway I generally find X1 workflow much quicker for me.......... in no particular order likes and what I think could be improved. ** With the proviso that there is a bit of a learning curve involved**
Envelopes - are much improved. I usually have several on each track (avg. 10ish) and always found pre-X1 annoying in that I'd end up moving either the wrong envelope or clip by mistake. NOw there's no chance of that, switching 'modes' is quick and easy thanks to shift+click, I don't even need to think about it. Could be improved by having a popup on mouseover on the ghosted envelopes. It's quite hard to tell the colours when they are ghosted. The popup will IMHO make that part just about perfect.
Screensets - These really are THE big difference. Think layouts on steroids. They remember everything snap, hidden tracks, open windows, edit filter settings, etc. etc. - there's 10 of them recalled almost instantly. If you can imagine having 10 independant instances of the same project open where the only common thing that can't be changed is the now time position and that's pretty much it. Fantastic, only limited by your imagination. Improvements - more of them and a easier way to load and save indivdual ones from a library or manager.
Smart tool Love not having to change tools hardly ever. The only tool I use in addition is the mute tool for comping. Would be better if there was a degree of customisation but it's set up more or less how I had PRV 1 in pre-X1 anyway. It's great not having to think ok I'm in the PRV, gotta change tools, or now I need the select tool etc.
Multidock no more windows that need to be endlessly cycled through or hidden with the mouse. Open a window dump it in the multidock, tab through them with ctrl+shift+arrow key. Hide the whole lot press D.
The whole thing of hiding stuff with keypresses is great. C control bar, I Inspector etc. I just don't see the complaints about how much space each part takes. It hides and shows instantly anyway. I guess pressing a key is hard work though.
I'd like to see the inspector remember it's narrow setting though as a default if required. The control bar could be better thought out. Perhaps collapsible modules maybe? I don't really use it much other than as a state indicator but I can see why it would annoy some who want to see all the modules and use mouse/icons a lot
X1 seems to be like marmite, love it or hate it, there's not much in between (apparently)
Colour customisation isn't good but I've never customised much. I'm making music not a praticising graphic designer.
having said that my only real wish there is that the current track colour change would stick.
As I said though, stability, it is the most solid Sonar I've worked with though in fairness V8 & 8.5 were pretty good for me as well. There are many others having problems though, seems to be luck of the draw. I don't think machine age or firepower is the issue though as my system is a bit long in the tooth now.
I wouldn't take my word for it or others on here though. Run the demo and see how it works for you. Only thing I would say is give it a fair run but think of it as a new program that is loosely based on the Sonar you know. I've found 99% of the changes make sense once I'm used to them.
***** All of the above is IMHO of course.