co2 is going to only get worse with the winter, Air would seem the best bet
There are a few threads on this.
Where tournament is the game of choice the chances are that you won't want to be using a co2 capable gun
In a few cases co2 is best - and in some of them liquid co2 is what is wanted, so the colder the better
If the site you play at only fills co2 then that is what you want - and an appropriate gun
Otherwise air is pretty much the preference
And with regard to filling - get your fills from the site you play at