Hysteria2
The essential thing about Hysteria2 follows not from its feature list but from one quirk of TCP. When TCP loses a packet it treats that as congestion and slows down — logic designed for wired networks, where loss really does mean a jam. On mobile networks and long routes packets are lost for other reasons: interference, a busy hop at the carrier, handover between towers. TCP cannot tell these apart and cuts speed on a link that is in fact free. Hysteria2 runs over QUIC, that is over UDP, and paces itself without inferring congestion from a lost packet. On a clean line the difference is negligible; on a poor one it shows immediately.
In short
Hysteria2 is the pick where the line is unstable: mobile data, a long route, evening hours with packet loss. On a steady link it is no faster than the rest and sometimes slightly heavier. A separate limit is UDP itself: some networks, notably corporate and hotel ones, pass only TCP, and there the protocol simply will not come up.
Frequently asked
Why is Hysteria2 not always faster?
Because its advantage only appears under packet loss. On a steady link TCP does not cut speed, so there is nothing to win back and the difference falls within noise. Switching pays off when throughput drops in bursts, not when it is merely low.
What if Hysteria2 will not connect?
Most likely UDP is closed on that network — common in hotel, corporate and guest Wi-Fi. The check is simple: if TCP-based protocols work on the same network and Hysteria2 does not, that is the cause. The fix is to switch to a TCP protocol; the same subscription carries them.