It seems you are asking which video fromat produces the smallest file sizes.
The simple answer is the one using the loweset resolution: 4. WVGA 848X480.
The degree of compression will also affect file size (and image quality). Higher comression gives a smaller file size but lower quality.
Page 5 of the manual tells you how much data is generated per hour. You DID try looking there, didn't you?
Manual here:
http://marketing.prestigio.com/$Customer_Support/Manuals/Car_video_recorders/RR320/PCDVRR320_MANUAL_EN.PDF
Page 5
See also page 3. You shouldn't have to worry about filling up the card. You can set Loop recording which lets you set the video duration (1, 3, 5 minutes or off) for loop recording. When the microSD card is full, the device will delete the oldest unlocked video file automatically.
RTFM
July 2016