The best camera is the one you haven't bought yet
I guess it depends what lenses you're thinking of if the small weight/size differences stack up vs. the increase in cost etc. We're always chasing that size/performance/cost trade off.
I've always wanted the smallest possible body so I can use the smallest possible package if I want it - but as I seem wedded to the 12-40 PRO these days I could probably go the M5 or M1 without really noticing the bigger body. I've not yet hit the limits of the M10ii, it's me not the camera so I'm content to stick for now.
If it dies I'm not sure what I would go for next.
MPB have several "good" E-M10ii for £165 each.- E-M5 iii start at £734 - with those kind of price differences I'd be tempted by an M10ii and a lens or two.
I guess if by "walking" you mean "getting soaked" you might do better with one of the weathersealed bodies though
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