I have the first version of this lens.
More than happy with it.
I don'[t think they altered the optics in any way from the first version to the G2 version.
I have briefly played with the N24-70(non VR) and more so to experience the difference in focusing speed/accuracy more than sharpness.
Didn't compare sharpness as the N24-70 was mounted on the owners D750 and I have my T24-70 on a D800E.
But the Nikon lens focused microseconds faster and more positively.
My version of the is plenty fast enough for my tastes, and I think Tamron did update the focusing ability in the G2 lens too tho ..
I'd be pretty sure that you wouldn't be dissapointed with the Tamron lens as a purchase.
My only gripe with the Tamron lens is just the physical design of the body.
On my D800(and D300) I use a bluetooth adapter that fits the 10pin port on those bodies.
With every other lens I have(and other's I've quickly tested too) the issue has never come up, but what happens with the Tamron 24-70VC lenses is that to mount this bluetooth adapter to the 10 pin port, the lens needs to be removed first(same goes if the adapter is to be removed too).
This Tamron lens design has a very large bulge for the switchblock(for AF and VC) and it leaves minimal room in front of the 10 pin port and flash sync port on those body types.
I no longer have the Nikon MC36 remote, but I think it also impeded fitment and removal of this plug too(but still, only just! ... allowed it to be mounted/removed with lens still attached).
The remote I use now has a much slimmer attachment plug for the 10pin port, so can be removed a little bit easier.
Note that this issue is not really so much of an issue, and in some ways it's a bit of a bonus(in that the bluetooth device will never fall off and get lost with the Tamron lens attached!
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It's just that this lens is the only one I've ever tried that does this, so when removing the Bt device I forget that this happens when this lens is mounted .. etc, etc.
For all intents and purposes it's a great lens.
I haven't had a lot of time to do photography recently, and from memory the most use I've had from this lens has actually been doing video all day a long time back for a street event.
I was collared into doing some stills for this day(family!) .. and when I got there the person also rounded up to do video couldn't make it, so I was forcibly reallocated the role of video0ing for the day instead.
I wasn't prepared for it tho, no tripod barely any gear gear etc .. but I did use the T24-70, and having the VC was a massive bonus needing to do the video hand held all day.
Took approx 3 hrs of video, with VC on all the time.
The AF motor was never heard through the sound( I did have an external mic tho) and the VC worked a treat.
In a sense it 'saved the day' for my sis's needs on the day.
I suspect that the G2 version would be at least equal to the first version if not better.
And I've thought of updating to the G2 lens(aas well as getting myself their 70-200 G2 lens too) .. but I just don't get enough time to do photography .. so it wouldn't be money well spent for me for now.
I'm not a regular pixel peeper, but the D800E doesn't really stress the IQ of the this lens in any way.
I also have the older Tamron 28-75/2.8(still!) and by comparison that lens is stretched a bit in some instances(lens settings) .. plus that it's always backfocused on all my cameras at 70mm!
I also have the Nikon 24/2 Ais and the Tamron at 24 is definitely sharper across all aperture values up to about f/5.6 or so where they've equal.
I like the Nikon 24/2 tho as it has a nice rendering for some situations(less contrasty).