I like high torque setups over high speed. A combination of high torque gears + high torque motor will give you much quicker trigger response.
The one thing that's always irked me a bit about AEGs is that delay from the time you pull the trigger (especially in semi-auto) till the BB actually fires off. For full auto, it's not much of an issue, but I like shooting in semi, I like it responsive. The delay, of course, is because the motor needs to spin up to speed, overcome the force of the main spring, etc. Unless you have a shit battery or motor, you're talking about a fraction of a second, but it still bugs me.
So the higher the torque setup you have, the more power can be brought to bear on the spring more rapidly. A mix of high torque gears + motor will make the trigger response almost as snappy as if you were firing a GBB or real steel. You can never get rid of the delay completely, but you can certainly minimize it.
The down side of a high torque setup is it reduces your rate of fire due to the motor spinning more slowly. To me, this isn't an issue. I would prefer have a more realistic rate of fire over a BB hose, and I value trigger response time over rate of fire.
My personal preference and recommendation is Modify SMOOTH Modular high torque gearset + Guarder Infinite torque motor. Or if you want the high torque but like a bit higher rate of fire, the Systema Magnum motor boasts both high torque and (relatively) high speed, so you can more or less get the best of both worlds. Of course, having the Systema name on it, it's expensive.
There are other factors too as to when you shoudl or shouldn't use speed / torque setups, but I think this is a good start.
Good luck.
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