From our experience it is best to have the smallest classes of scans, so rather than scan /14 or /8 which could be a lot of hosts, scan at most /24 (class C) and have several of them run at the same time.
This gives the following advantages:
- Finishes quickly, if you scan /8 it can take hours, or even days to complete - while having several /24 will allow you to see the results more quickly - there is no benefit in scanning more hosts, the results are the same if you scan 2, 4 or 10 hosts
- You can run several such smaller scans at the same time window and use this to maximize your scanner's capability - the scanner by default scans up to 8 hosts in parallel - combining several scans can give you more per second tested host than one scan
- The results are easy to combine even when the scans didn’t occur at the same time
- Smaller's scan time window can be more accurately controlled, most scans of /24 take about 1 hour to complete, while /8 scans' scan length varies a lot more