I used an Ingen 5. It is a puffer. So the first thing you need to think about is if you can use a puffer. The good thing is that it goes up to 6 liters. It is able to go on the airplane, so that isn't an issue as well. I would suggest getting the double batteries though. Also it came with a car charger and it can charge and be in use at the same time (just not on the car charger). I would still switch over to the hospital's oxygen when I had appointments, since the ride to the hospital was about 1 hour and most of the time I was on 6 liters. It is also only 7 pounds with the battery and not that noisy like some of the others. Downside I believe it costs a little more.