Most of them look like lazy positions. 6 looks straining on the neck, 8 just looks wrong, 11 can give you a hunchback, 2, 6, 7, 12, 13 and 14 aren't really good for maintaining sperm levels because the radiation emitted can affect them (you may think wth but this is a true fact actually), I don't know how people can manage 9 (I mean youre not swimming exactly). For me however, 16 seems decent coz its more of an upright position and as long as the machine's not resting on my lap but on a table instead but of course, each to their own opinion. :)