They're both good mice but different, the G400s has a more capable sensor (max tracking speed), other than that its subjective. If you want a simple mouse go with g100s, if you want side buttons and more of a palm grip mouse go with g400s.

g100s

I use it on Razer Goliothus

They are completely different. Choose whichever's shape and weight feels right for you.

wmo

fuck ur wmo

g400s.

g100s vs g400s?

stupid question, these mice are different in any way.

the answer is definitely up to you.
Because its mostly about the shape and weight.

when you take off the weight from g100s, its so light, but g400s is always heavy.
and actually as wmo user for around 10 years I guess, I cannot use g400s, it feels soooo heavy. So try both if you can. If not google for their comparison pictures and specs.

btw both of them has stable sensor, so please do not look for their max tracking speed or whatever. I have tried g100s for couple of months (now im using zowie FK) and just couple of times it did weird things (when I moved it really fast, but i dont know if its my mouse or a general issue)

as far as I know they both have good sensors. I dont own a g100s but I can tell you the g400s is pretty big and pretty heavy

I like that about this mouse and prefer it to smaller lighter mice, but it depends what you would rather. Big heavy palm mouse or small light claw mouse

the g400s has the same usb problems that the g400 had. just google g400s usb issues or check the logitech forums