which generates more efficiently, single or 3 phase systems
I want to build a hand crank generator for my travels and I am curious if there is an advantage to a three phase &quot;motor used as generator&quot; design or if it will be around the same output to a similarly rated ac motor or even a brushed dynamo.

A three-phase generator has an advantage over a single-phase one in that the load on the input - you in this case - remains even throughout the whole revolution. The single-phase will have high resistance when the sine output is maximum and low resistance near the zero-cross.
The DC brushed generator will be even as the brushes and communtator maintain the same relative position between the magnetic field and the excited winding.

I recently tried using a super potent rs775 with a nice long lever and high gearing ration of 1:160 but boy getting 20 watts (per hour rate) is hard,

First we have no idea what a &quot;super potent rs775&quot; (sic) is. You should explain and provide a link to a datasheet.
Watts is not measured in &quot;per hour rate&quot;. Instantaneous power is measured in watts (W). Energy is power by time and this is generally measured in watt-hours (Wh) or kWh.
You should be able to sustain 100 to 150 W power for hours when cycling or other work. 20 W seems about right for a hand-held generator. A two-hand crank arrangement similar to bicycle crank would probably allow a higher output as the arms can thrust against each other.

i could barely do 15 min. yet I saw this one small 25 watt generator review online with a lever half my size and was matching my output. I feel dumb almost, that they managed to do more with so much less. they had a small 3 phase generator with a much lower gearing.
So is this possible because of the 3 phase motor?

More likely due to measurement trickery. There will be some differences in efficiency but not much. With the lack of details in your question it is not possible to answer.