I agree, working out in a gym eliminates a lot of factors (wind, uneven courts, non-regulation dimensions), that would be my first option as well.

But there is something to say about being out in the driveway outside training once in a while...good luck!

id have to say the gym even though 95% of the time i play outside (mainly because i do not own a membership to the gym) but at a gym you can work on layups better and the lines will help you get that court feeling so your more familiar with it when you play in games if you play outside your whole offseason the gym is just gunna be a familiar face when the season starts back up when it should be like your best friend or the backside of your hand something along those lines. but id have to say the gym is a better place to play because the hoops usually hang from the ceiling so you can do layups and what not the lines are official and you dont have to ajust your shot depending on what the wind is doing, you also can play when its raining and cold and what not

I'd always prefer to use the gym, but, there are a lot of times that the gym is not available and the outside courts have the heavier competition. You do gain a little more toughness on the outside courts.  You always worry that you might be risking injury, but, the same could happen in the gym.  I will go where ever there is ball to be played.