It's sort of depends on what you mean by whom? Manufacture wise I actually had some great luck on my 3.1 with rainbow heavan. They are a fasttech supplier and are often sold with red rings. My EHPRO ... SUCKS. I can't emphasis that enough. But v2 from Ehpro was excellent. Fastech also sells another 3.1 that is pretty good because they use tight o rings. The pic I've attached shows the difference. From left to right; Rainbow heavan, Fastech, EHPro and SvoëMesto View attachment 32382
I got my kayfun's off amazon, and they are very good quality, haven't had a problem in 10 months, bit more expensive than other dealers tough.