Win10-Hater

I used Windows 10 on my Dell Inspiron 15 3567 (my secondary laptop) with an Intel core i3 6006u, 4 GB RAM and a Toshiba 5400 rpm HDD, and it was eating up all it could, it was horrible!! Now I have Windows 8.1 (I even used Windows 7 on that laptop) and it is very fast compared to Win10 or even 7. Don't you think?

8.1 is surprisingly well optimised, it's probably the best out of the NT 6.x line. Vista SP2 comes in second place I'd say. But yeah, 4GB RAM and a 5400RPM SATA drive on Windows 10 is just asking for trouble due to the invasive telemetry querying things as well as the pagefile being in constant use.

8.1 is the perfect mix of traditional and modern stuff. It has many useful features such as fast startup, delaying updates up to 2 days etc. Vista is the second best only by a really tiny margin to me too because it does not have fast startup (but I don't really need this as my primary Vista laptop has an SSD) or delay of update installation of up to 2 days (only up to 4 hrs). 

Otherwise, Vista and 8.1 are equally good to me.