I've tried many, can't go wrong imo. There are differences but I also wouldn't spend big $ on rare tubes. My longest lasting so far is probably a vintage Japanese tube, they bought Mullard's equipment and made tubes with seams on the top, the getter is black which denotes a very good vacuum.
I've had a couple of old stock go out on me too, but they were used tubes with questionable history.
In my Audio Research 5SE, the 6550 lasts about 2,500 hours, while the 6H30 that accompanies it, can reach 5,000 hours. Don't have an estimate for 5AR4 NOS in a preamp PSU?
A NOS Mullard 5AR4/GZ34 should have a very easy life in a preamp, should last almost forever. Preamp tubes draw very little B+ current.
The new 5AR4 tubes from China and Russia are hit and miss.
I think it was GE that made a 5AR4 tube as well, it's easy to spot as it has 2 copper rods that the plates attach to. I've heard good things about that tube as well.
I have been said by a reseller that 5AR4 didn’t extend much beyond 1000 hours. Another specialist explained that it was not how many hours that was important, but how many times this kind of tubes light on and off. For a 6X4, he explained these tubes were done (military grade) for about 4000 light on.
as long as you keep the values for transformer internal resistance, charging capacitor or choke and the maximum current. Then the tube will survive you. there are plenty of old radios and amplifiers that still work after fifty years.
If you're looking for a reliable, cheap 5AR4/GZ 34, take these export tubes from East Germany, mostly made by RFT or (Sovtek) where they were still good. Definitely better than today's new tubes.