For an electronic computer you also need a source of electricty -- and debugging is going to suck without a voltmeter, oscilloscope, logic analyzer or even LEDs.
I'd go mechanical any day. I recall the Soviets had a computer based on liquid that could compute certain differential equations.
There was a mechanical Turing machine shown at Makers Faire UK. Supposedly it was built only using hand tools and scrap parts. I'd say that's close enough to a hand-built computer.
I'd go mechanical any day. I recall the Soviets had a computer based on liquid that could compute certain differential equations.