nikon - How do I choose which 24-70mm lens?

This is not 'which should I choose?' but 'how do I make the decision?'.
My experience is quite limited, I've not had my first DSLR a year yet.

The closest I can find is Michael Clark's answer to Which lens is sharper? The Sigma 18-50mm f2.8 or the Tamron 17-50mm f2.8? which points out things between those 2 lenses I wouldn't have even known to look for.

My criteria are
approx 24-70mm
f2.8
'sharp'
after that I'm at a bit of a loss

I want it to cover my existing, but soon to be sold, kit 18-55mm & Nikon 24-120mm [which I don't like much at all] but am not interested in going wider than ~24mm for now.

I tend towards portrait & macro photography; lots of light, tripod & remote shutter release. I like bokeh, or to be more precise, I like out of focus backgrounds with clear emphasis on the subject.
I'm also, for this lens, hoping to use it as a general-purpose walkabout, just in case. The 24-120 covered that nicely, but it doesn't really satisfy for my studio work.
I have a 70-300mm lens I am satisfied with for longer ranges.

The choices as I see it are

• AF-S Nikkor 24-70mm f/2.8G ED at approx £750-1000 - lots of choice on the used market


• Tokina AT-X 24-70mm F2.8 Pro FX - £675-900 - little choice of used, lower market presence altogether so opinions are thin on the ground..


• 
  

  Tamron SP 24-70mm f/2.8 Di VC USD - £600-800 - fair choice of used.

  
  

  & the rank outsider right now

  
  
  


• Tamron SP AF 28-75mm f/2.8 XR Di LD Aspherical IF Macro - approx £200 used.

I'm assuming that based on price alone, that's about the correct order for quality.

Ken Rockwell seems to like the Tokina, & I like what he has to say about it, even with the negative comment that it's bit slow to focus.
The Nikon would seem, though, to be the best bet... as it's a Nikon, if for no other reason.
The Tamrons, one pricier than the other so let's assume the cheap one will be... cheap.

Of course, no-one can choose for me - but how do I go about making the decision? Trying them all out at home is really not an option, so I'm going to have to choose from 'spec' & 'reviews'.

Maybe I'm looking for the "gotchas", the 'I wouldn't use abc for portraits', or 'watch out for the xyz at longer lengths'; 'the abc is soft at the edges'... 'the QC isn't so good & you can easily get a bad one'...
or maybe I'm looking for a simple, reinforced statement - 'you can't go wrong with abc for the money, don't waste it on xyz'...