Starting with FC3 is a good start for sure :)

The opinions are always split when it comes to pick the favourite from a series.. you can see that in the previous comments left on this post where someone said that no other game released after Far Cry Primal was better.

But I guess it all depends on the gaming preferences everyone has and what your expectations are from a game. Personally I found something nice in each game of the series but only some of them turned into my favourites, fc6 being one of them for sure :)