The main difference that separates the SJM valve with all the other bi-leaflet valves is the "pivot guards". That my friends is why the SJM leaflets open fully, every pulse, at any mounting angle, at any pressure.It appears to be a bit longer both ends.
A picture from my blog (couldn't quickly find it in their literature)
After the SJM valve came out everyone else said "we can do that to" and they sat down with their CAD machines and started with a tube, however just because you have 2 leaflets hung in an orifice doesn't make them function perfectly. So ... I will leave it at that - the catch 22 is I have proof but cannot disclose it - I prefer not to get sued, everyone has their favorite (Ford vs Chevy) so take your pick and be happy with your decision.