No exercise will help you if you sit 8 hours a day, 5 days a week. Think about it. You may go to the gym (or exercise at home) 3 times a week for one hour, this is compared to 40 hours a week of sitting.
Recent studies (see eg. this article) suggest that the most effective method is to interrupt sitting often. Standing up from your desk 35 times, spread throughout the day is much more effective at reducing the bad effects than sitting without interruption and then do an exercise program with 35 squats.
It seems that the optimal strategy would be to incorporate a lot of non-exercise activities in your day, supplemented with an exercise program, which can be any sport you like and are motivated in.
Many people will argue that exercise X is better than exercise Y and they may be right, but the truth is, to change your lifestyle, it is not enough to add a few minutes of training before/after your day. You need to look at the how you do your whole day and optimize that. Stand up from your desk at least once in every 30 minutes, stretch your back, arms, legs, a few jumping jacks, a push-up maybe, anything you are able to do.