Kindly I am looking for your advise on which software release to choose (Amsterdam-17.3.5 OR Gibraltar-16.12.5) if I want to upgrade Cisco ISR4331/4221 routers. Both are recommended S/W releases, although Gibraltar consumes Smart-license which we are not using currently.
Thanks & Regards,
Personally i would go to 17.3.X version that is moving forward, eventually you need to go that version, soon or later 16.X going to be end of Life.
read the release notes :
here is smart License :
You can contact License team to conver the License for you.
According to my experience with TAC, I think the obvious version is the newer one. We know however that the newer the version more risky as we dont know what we are about to face in terms of bugs.
So, my advise is if you are already running a version and it is stable and you are facing no problem, keep the version. But, if you are building something new or need some specific feature, then go to newer recommend version.