Obviously, bottling from a keg is what you have to do if you kegged that particular batch.
But wanting to enter a beer in a competition is irrelevant to whether I bottle condition a beer or keg it, except if the beer is still in a barrel or conical and a competition is coming up soon. In that case getting it reliably carbonated in a keg first and then bottling with the Beer Gun is the way to go. I won't enter beers that are not already carbonated exactly how I want them before they go out the door to a comp.