Up to you, but here is some advantages of each:
(both have on/off; both come in a variety of colours; both have two standing positions)
Yoobao:
Leather - looks expensive - doesn't smell
Slimmer than STM; this is negligible
Covers all (top / bottom) - acts like a layer to protect iPad
STM Skinny
IMO nice fabric - not leather, but feels nice and is your personal opinion
More protection for corners - if you drop it on the corner there's more protection than Yoobao - but the bottom and top are exposed
Still slim, but slightly thicker than Yoobao, so more protection - negligible though
Yoobao is good to protect your iPad from scratches; STM can get scratches because of open top / bottom, but it will protect iPad more from drops, because of corner protection. Yoobao and STM look expensive. if you can afford it and would like the STM but I leather check out
link.