I've been using Cakewalk sequencers since CWPA6 (maybe earlier, but I still have these floppies on the shelf!). I found the transition to the first version of Sonar to be difficult, and then it smoothed out for several versions, until Sonar 8 (again I think that's the one, it's been a while).
I found the transition to X1 to be cumbersome. In contrast I find the transition to X2 to be almost non-existent. It isn't that they didn't make some significant work-flow changes, but rather that the changes seem to align well with the way I'd like to work. I also think they are getting really good at documenting the changes in their videos.
As Karl pointed out, if this is your first DAW platform you will have a lot to learn. If you are coming from DP or PT you'll also likely find the learning curve a bit steeper than if you were coming from Cubase or even Studio One.
Before I upgraded to X2 I did try both Cubase 7 and Studio One 2. Oddly enough, I ended up purchasing a license for Studio One - I like it, and while it won't replace Sonar for me, it is a nice supplement, providing me with an alternate approach when I need it. (FWIW, I still use both Sound Forge/CD Architect and Wavelab for audio editing and CD authoring. Two very different approaches, and sometimes you need that.)
To answer you last question, I'd suggest that it is a toss-up between Sonar and Studio One in terms of simplicity. I think they both have too many menus<G>! But on both cases the arrangement of commands make sense to me, so I really don't think one is easier than the other.
There are fully functioning trials for all three - might be worth a little woodshedding to help you figure out which one is the best fit.