First off, where are all of the alleged 'experts' on this board?
Creampuff, there is not a simple answer to that. Version 2 1090ES is still in the works, as are the associated parameters.and it is likely that by 2020 it will be version 5 or renamed.
Ver 2 UAT is also in the works. As noted in previous posts, 1090ES and UAT ac cannot 'see' each other. Consider that when the FAA states alt for 1090ES/UAT. I have not heard of a combo 1090ES/UAT system out there, so that should tell you where all of this is going.
What to look for is the parameters and equippage associated with V0 vs V2 et al.
The US mandating V2 (so far) is significant. The ac must have the equippage and redundency to provide the paramters required.