For warm water, ie with little weight, I prefer integrated - it keeps things simple. However, I also dive a lot in very cold conditions, using a dry suit and plenty of weight. Integrated means far too much weight on the jacket (uncomfortable, difficult to carry out of water), while a belt is not safe (I've had a near miss with the belt around my knees), so I use a harness instead. It won't drop off, but you can ditch weight quickly if needed; it sits just below the BC so it doesn't get in the way; and out of water the weight is supported by your shoulders, not your hips. In short, if you need little weight, integrated can be best, but if you need a lot and don't want to bulk out your BC, try a harness.