While Biggles is right that the Krome hasn't changed all that much since it's introduction in 2012 (i.e. the EX update was modest), it's still a lot newer than your other options, if those are the only three you can choose from. Whether newness is a factor for you is a whole other question. Newer sample sets tend to be more "real" sounding when it comes to acoustic emulations, and may have more sounds that are/were trendy for more recent music/sub-genres.
Overall, differences among the Tritons are descibed at
https://en.wikipedia.org/wiki/Korg_Triton - of the two you mention, I don't see any reason to not choose the Exteme, as it would seem to have all the capabilities of the older models and more.
One other consideration is that playing the 61's semi-weighted keys (Krome) is a very different experience than playing the 88s on the others (and also, if you still might gig with them, the travel weight is very different). Though you'd also have the option of playing the 61 from the keys in your Juno DS 88.
I had a Korg Pa700 arranger and loaded the Triton packs into it, very impressed even if they were of a smaller sample size than the original.
The Triton packs actually have a sample size of zero. They are recreations of the Triton sounds using the wave samples already present in the PA700. In some cases, the exact same old Korg samples may have still been present in the newer instrument; in other cases, they would have used the PA700 waves that were most similar.
In the case of the Krome the Triton and M1sound packs can be loaded into it so you can get three keyboards in one.
The Triton pack for Krome is not a complete Triton sound set... it is a 128 sound "best of" collection. And similarly, no new waves are loaded into the Krome. As with the PA700, they are patches created using the same waves that are already in the keyboard (which may or may not be the same as the original Triton waves).
However, the complete Triton sound set, with all its original wave data, can be run as a computer VST, see
https://www.korg.com/us/products/software/kc_triton/