the second monitor,1280 x 1024 is on scaled because when "best for display" has chosen it gives 800 x 600 resolution
am I missing something? does VGA works in 1920 x 1080?
If you open the Display pref pane, you SHOULD get a Displays pane in each display.
The name of the window SHOULD reflect the name of the display (something like Samsung 2333HD)
Do BOTH windows show the same name? I bet the one connected through VGA just gives a generic name, like Display ...
Yes, VGA SHOULD work at 1920 x 1080 (assuming your cable is good, which I doubt

)
I am using the same mini as yours.
I first used HDMI to VGA. The display worked at 1920x1080, but did not talk to the computer properly - display sleep, for example, just didn't work.
I switched to HDMI to DVI, and display has all functions, and the screen is noticeably sharper. Expected, because VGA is analog, and the DVI is a digital signal. Seems likely that your VGA cable is not providing what it should.
Change your VGA connection to something else. Mini DisplayPort to DVI would be a great choice.