Please just bear in mind that marketing practices have no bearing on how good the actual product is. On-X had some of the most outrageously outdated and misleading statistics posted on their dite, last time I looked. Makes me sick to think people see that. Almost all of them go out of their way to show their competition in a bad light, no matter how abusive the method. Part of the reason St. Jude took so many years to bring their tissue valve into the US market is that they had been poisoning the well so savagely for all their tissue competition for so long, they couldn't think of a way to market it.
Try to judge the products on their own merits and features, rather than on "comparisons" you view on their brand websites, or things you hear about their sales and marketing people. If you are minded to, you should choose and insist on your choice of products. As often as not, the surgeon will advise you to use the one he has in stock, not one that is necessarily perfectly chosen for you. In their defense, many tend to think the brands are basically interchangeable.
Best wishes,