Just stumbled onto this post and thread and made me think back 6 yrs. - I was 58 - 293 lbs and was discovered to have 3 blockages in my heart. Today I weigh 178 and ride 4 to 5 thousand miles a year to include centuries. Great advice in the thread - looking back let me give you some hindsight observations. My doctor sent me to heart re-hab first where essentially the message was exercise based on target heart rate. I then moved to the gym and became fairly dedicated but an hour on a stationary 4 times a week gives a new definition to boring. I did see weight loss results but I sincerely believe that exercising beyond 40 or 45 minutes is when you start to fat burn. Now to your question, flat or hilly? I split time between a flat and hilly locations but started out doing biking on the flat and from the starting point that you and I come from, I believe flat is better because it is easier to get a steady heart rate and that will be important when you start. Biking in my mind is the answer for weight control because as you enjoy the sport more it will be increasingly easy to get 2 hrs. of aerobics without the boredom of the gym. Good luck with it. I lost 90 lbs the first year and the next 25 lbs over the second year.