JMO but as the owner of several clones gathering dust in a rack..... if i had it all to do over i would buy something with as low a voltage drop as i could with a self adjusting or adjustable top pin.
In short, an all brass mech mod. Virtually all of the all-brass mods lose less than .01v through the mod.
Pretty much any stainless steel mech mod is going to lose a minimum of .02 volts and most are closer to .1v loss. The Nemesis is among the best here, losing only .03v even with an 18650 battery. However, if you use that gold colored kick ring in the middle it suddenly jumps to a .12v loss.
Among the worst mods for power loss through the body are the GGTS and the Segelei #20, with a loss of .48v and .69v respectively.
To the OP, since you're bound to ask this now...
The Natural = .34v loss
Magneto = .04v loss
You'll get a much better hit from the Magneto.