Yours 16**** seems newer. It's hard to say which is more stable. Usually newer firmware would have some bugs fixed and new feature added which can be found from the note of each firmware on the tplink website. What's the problem of your D9? Sometimes firmware update is not a fix.

Problems encountred are :
- Poor connection stability (sometimes the connexion went out or does not repsond quickly)
- Sometimes when trying access to the admin interface (192.168.1.1), it shows me the ARcher D7 old blue-ish Interface.
- Signal is not as strong as expected (i bought the Archer D9 because of his large covering with the 3 antennas).
Have you encountered same problems ? and what firmaware version have you if you have this same device ?

Thank you.

That wired. How come D9 will show D7 interface? Have someone flashed your router with a third party firmware?
When connection went out, check the LED. If DSL led went down, contact your ISP to check line. If internet led went down, contact tplink support