If we look at what is written in flash (6 volts) it seems that alkaline batteries are better than NI-MH, because alkaline nominal voltage is 1.5 volts each, while Ni-MH batteries have nominal voltage of only 1.2 volts each one.
The problem is that this nominal voltage does not match the use of high current in a short time. In fact, alkaline batteries, measuring 1.7 volts when new, but at the time much energy is drained drops to approximately 1.1 volts.
Batteries NI-MH actually has 1.45 volts when they finish loading in a high quality charger, but when too much energy is drained, drops to 1.2 volts.
This explains why the recycle time is faster with NI-MH batteries of good quality. The actual voltage at the time of high consumption is higher in Ni-MH batteries, even if the nominal voltage is lower.