There's like a zillion free software tools to monitor signal strength and channel utilization/saturation.
I'd like to hear recommendations for the best one to use on a Windows (8.1) laptop with an internal 802.11ac card.
I don't believe that InSSIDer measures channel utilization (busyness). This is infinitely more important than signal strength.
Layperson's Analogy:
You're on a bridge atop a multi-lane freeway.
Lanes correspond to WiFi channels (non-overlapping channels)
Car speed corresponds to signal strength
Volume of cars (traffic) corresponds to channel utilization.
So your ease of access to a lane, and travel time, is more about volume.
A neighbor streaming HD 1080 on WiFi presents far more volume and negative impact than does a large number of neighbor-WiFi used little, or used only for web browsing and email.
I haven't yet seen any freeware that measures channel utilization. to so so, you need to run data collection at the worst case time of day (after dinner hours for residences) and dwell on all the channels for quite some time to build statistics. And weekends differ, etc. The pros put in a monitor for days.
And then hope it isn't vastly different next week. Alas, such is unlicensed band wireless.
Fortunately channel utilization hogs are rare.
The WiFi SSID listing programs are usually just catching the SSID broadcast data frames - sent by WiFi access points (APs) or the AP function within a "WiFi Router". The SSID broadcast is normally 10 times a second but the transmission time is perhaps a few microseconds - corresponding to say 0.001% utilization. So looking at these SSID broadcasts' signal strength says little.