I am not sure what everyone is complaining about on Win 8.1. I use both desktop and laptop with 8.1 and i do not see any issues or usability problems at all. In fact, i find 8 is a lot better than Vista or XP.

in fact, 8.1 is better than Vista or XP (i have never use 7 because my last OS before 8 was Vista and i upgraded my desktop using the $25 promo MSFT had back then). My desktop is at least 6 years old.

as far as online account vs local sign in, the only disadvantage i can think of using online is privacy. With everything is sync at OneDrive, MSFT knows what you been doing, when you login, when you logout, when you standby your PC, i think it can create your usage pattern. For me, i use local sign in for both desktop and laptop