In a word:  depends.

Depends on what you are using it for and the environment in which you are using it.

I would start with a -14 and get proficient with it.

If you feel like you need "more", add another -14 to make a dual setup.

If you need even "more", try adding FLIR/Thermal to your setup.

This is literally what we did:  had the choice of -14s or ANVIS and experimented with adding FLIR to the setup.

The best setup is FLIR/Thermal+NV...if you are mostly detecting/IDing "targets".  It's somewhat difficult to setup but I'm sure some commercial savvy guys (which I am not) will be along to recommend some methods for doing so.  Not, IMO, the best setup for conducting weapons engagements, but it can be done.  It also takes a little adaptation to enable your brain to merge the thermal and NV images.

Second best is dual NV, especially where depth perception is required like driving or the "A" in ANVIS:  Aviator('s).

If you think about your operating environment most of the time, is it zero illum/pitch black?  Zero reflection of city lights off of clouds?  Or are you in a city.

In my case, the answer is rarely is there zero ambient illumination...and under these circumstances, especially when using weapons, a single -14 is the optimal setup:  you use and see a lot with your unaided eye and fill in the shadows/darkness with your NV.