OP asks for "lowest latency" but HTTP is fast enough, and later in the thread says "perceptibly instant" is the goal. HTTP is going to be your slowest option, almost certainly, but even the slowest solution is "instant".
What exactly are you trying to do, OP?
(Esphome seems like the answer you're looking for. It's faster than MQTT and you can program parts of the automation and service management in the ESP hardware. RF is probably the only way to go faster.)