I, too, like Mixbus very much but I work with midi so much and the midi editing in Mixbus is terrible. I use Mixbus a lot for tracking live audio projects.

Spend a couple weeks with each demo.  Decide what works best for you.  It's probably good to have a 2nd (backup DAW), just in case, or for creative purposes.  But beyond two DAWs, it's going to be a real time burner.  I'm trying to stretch it to 3.

I brought Presonus Studio one 3.5, Samplitude Pro X3 and Tracktion Waveform 8 when Sonar exited the scene.
I didn't register Studio One until 4 came out and I got Studio One version 4 upgrade for free. I'm glad I did get the extra ones. I like Tracktion for what they are doing and it is a great scratchpad DAW. Samplitude reminds me of Sonar 8.5 layout in a way and I really like that Samplitude so far has not forgot about folks with bad eyesight. (that would be me) I'm really glad I got it last year at the sale price. Studio One I believe I will use it like Craig does for Mastering. I'm still trying to figure the DAW out. I almost got Mixcraft Pro 8 too. It is a very capable DAW but sanity won out :)
I also tried MOTU Digital Performer and I really did like it but with my eyesight I couldn't see myself long term with it. It was really hard for me to read the small typeface :(
 
Anyway I'm glad I got the extra DAW's. Playing around with them I learned that they all have pluses and minuses to them. I'm actually looking forward to see what Samplitude Pro X4 brings to the table. But I'm so glad Cakewalk is still alive. Now Noel and company get a hold of Don from Overture and cut a deal to upgrade the staff view pretty please.
 

Studio One 4 Pro currently has a Black Friday upgrade price of $74.98.  Can't beat that with a stick.  I say go for it.  I might have to jump at that myself.  
 
EDIT:  I see you mentioned you have the Artist edition, so you were right...the upgrade is currently $149.98.  That's still pretty good.  Look at it this way.  Even if you decided it didn't perfectly meet your needs, the project view is still a dream for mastering.  So it's not a wasted investment in any case. :)

InstrEd
I really like that Samplitude so far has not forgot about folks with bad eyesight.

I didn't realize this, but that may be a factor for all of us in years to come. Much of your question boils down to personal preference, but it seems to be hinged on SF12 for you. You may want to email them directly and see if they give you a response (never hurts to ask). Otherwise, both come with a lot of features, and for basic tracking/mixing it will come down to splitting hairs and your personal workflow. If you have already gotten your feet wet with both of them, checking out videos online may help you discover things you wouldn't find using them in trial/demo mode.

From what I remember samplitutude did not have drag and drop from the browser into a track like Cakewalk and SO4. Also controller hardware associations with vst’s could not be saved and used in the next song. At the time those 2 issues were limitations for me and convinced me SO4 was a better choice. Perhaps Samplitude has upgraded those 2 features, but I am not sure.

I didn't mention it, but I use Ozone8 for mastering, so the Project Page feature in S1P may not be as valuable to me.
 
I hope to spend some time playing around with both S1P and SX3 over the next few days and will get a clearer view of the right choice for me.

s1p appears to be crash-proof for me, at least versions 1-3 do, just about to grab the cheap upgrade to 4

You can't go wrong with either Samplitude Pro X3 or Studio One Pro 4.1

• I prefer Studio One's GUI.
• I prefer the editing in Samplitude.  The Object Editor is extremely powerful.

Both have fantastic "mastering" and layout features.

Go with Samplitude, you won't regret it, also get the bird line skins for samplitude, really cool stuff..