Although I would agree that pool or aquatic exercises are probably the easiest on the body, I think many important factors have been neglected.
1. Most obese individuals are low-income individuals and, therefore, normally lack accessibility to such facilities
2. Most obese individuals are not comfortable wearing clothing necessary to get into a pool. Making an obese person put on a bathing suit or even t-shirt and shirts can be stressful, emotional and embarrassing.
3. Keeping body temp down may help obese individuals to exercise longer in the pool. However, a slight increase of body temp with land exercises helps curb appetite temporarily, whereas aquatic exercises usually do not.
Taking all of these into consideration, I would not put aquatic exercises as a general recommendation for mobile obese individuals [unless I knew they had access to a pool and were open to wearing a bathing suit]. Instead I would say walking. This requires no gym membership, no equipment, no bathing suits and it will directly translate into improving their activities of daily living. To reduce joint and muscle pain, make sure they wear appropriate footwear [and replace when worn], ice after workouts and stretch before and after walking.
The first thing I would add onto walking would be functional low-impact exercises, such as diagonal chops, which can be performed with no resistance or with a band, med ball, dumbbell or soup can.
When it comes to exercises for obese individuals simplicity is key because if they are not compliant with your exercise program it will not be successful no matter how good you think it is.