Best = Total cost over lifetime (buying, installing, maintenance and final preparing for new replacement valve) divided by total lifetime.
All compared for different valvetypes for the special application at the special location at the special plant!
With this I am sure that your valve will not be best for any application anywhere. (And perhaps even not for yours??? - And I am really for the use of high-quality valves)
Several additional NEW triple offset butterfly valves ship with zero leakage. This is a requirement per API STD 598 for soft seat valves. So, test all soft seat triple offset butterfly valves before shipment. Other standards apply for fire testing requirements etc.
Lets determine whether this is now going to an offshore platform fabrication yard, a construction job site, etc. Those folks normally have to perform pipe leakage testing. Let's assume that those guys often use dirty water to fill the pipe. Assume that sometimes they let lots of water sit (or ship) within various headers etc. for a long time.
Guess the percentage of valves, whether triple offset, gate, ball etc. no longer pass a zero leakage test. I don't know the official details etc. My experience with this problem related to an offshore platform where I participated as a support engineer for over two-years in another country. Although involved, I did not head any engineers, construction technicians, commissioning or other startup type folks. All kinds of tricks were tried mostly with ball valves to move the closed position just enough that they worked. I cannot verify but my memory would suggest about 75-80% of the valves (mostly ball) were not zero leakage during commissioning and startup.
BTW my message mentioned having to perform pipe leakage testing. This is not valve leakage testing. What their event may normally be called is hydrostatic pressure or hydrostatic leak testing of the pipe. The valves are likely left open as the intention is to verify that the piping is free of leakage. See ASME B 31.3 sections 323 and 345. Although I don't participate, this often requires the piping test pressure to exceed 1.5 times the design pressure. Also, the valves are likely open with test segments blind flanged to test the piping for leakage. Thus the zero leakage valves may or may not be tested during the hydrotest. My project seemed to have valve seat corrosion due to the hydro test water left within the lines when the modules shipped.
Instead of looking for the definition of "Best" on the market, I should have been more complacent in my question. Zwick has been around for over 30 years and has gone into many extreme conditions for several applications. Steam, Petrochemical, Oil Refinery and so on. So when compared to Vanessa or Flow Serve Which one would come out with better performance and reliability. I understand that Zwick is more expensive, but isn't quality and safety worth paying for?
