Should I join gym for weight loss ?

Hello guys. I wanted to loose some weight in this winter break. I was wondering is it a good idea to get into gym for this. Or should I just stick to dieting. Also please recommend some good gyms for weight loss in doranda area (for boys). One more thing, I am very new to this gym scene, should I ask for a personal trainer to get weight loss and if yes what would be the price for the same. Thanks for any help.