I have 4.14 but I want to know which version or mod is best.
The sim has been around now for twenty years or so and has gone through so many changes it is hard to say exactly what is best because we all have particular favourites.

It depends what you want, again, everyone will have their own personal preference.
The current major mod pack here is B.A.T., based originally on the 4.12.2 version but now with many added updates that most would say actually supersedes anything before or likely to appear. It includes all the stock contents up to 4.12 and much of the further community made aircraft, vehicles et al, as well as much later stuff modified from later official patches.

Most of the modded content here at the site effectively stopped at 4.12, folks got fed up with constantly updating/backdating their creations as the official developers released further content so that is where we are, 4.12 essentially.
Other sites have made files available that will allow you to modify your 4.14 version but you would then need to find stuff that had been updated accordingly, some stuff works out of the box, some not, it would get very frustrating testing everything as you add it.
If you prefer to use the stock game then 4.14 is so far the latest version but if you want to mod it then stick to 4.12, or 4.09 and 4.10, these have been the most popular I think and had various packs built around them.
For a newcomer it is difficult for any of us to give you a definitive answer, but if you can be bothered to download then B.A.T has most everything.
Take care and be safe.
Wishing you all the very best, Pete.