WiFi Analyzer - This app is ad supported. It has a couple of handy views: Channel Graph, Time Graph, Channel Rating, AP List, and Signal Meter. Channel Graph is good for showing relative strength of signals of the networks nearby. You can change the settings to either display SSIDs with the same name as one or separately. Time graph gives a slightly more confusing look of the same info (you can change the sampling time of any of these in the settings). Channel Rating shows you the strength of the signal on a particular channel. The comparison is a good one and handy if you are trying to determine the best channel to set your AP to. Ap List shows a list of the APs their MAC address, the channel they are broadcasting on, and the signal strength (with a lock over the signal strength icon if it is a locked network). The signal meter is very handy. You can have the sound on or off (like a geiger counter sound), there is a blinking light to as well. The screen shows the SSID with MAC address in parentheses and a signal meter showing the strength of the signal - coded from grey to yellow to green. On any of the screens you can take a snapshot of the screen. You can also send the current scan results. This app also prompts to start wifi, or you can set it to automatically start wifi on start of app and stop it on exit. I liked the setting to stay on while the app was active, otherwise my phone would keep turning the screen off.
WiFi Manager - WiFi Manager is exactly what it says, a manager. There is nothing particularly spectacular about this app. It shows the SSIDs, whether they are open or not, if not what type of encryption, State (connected, favorite, etc), Channel, Signal Level. You can choose to show only the live networks or all known networks. It can sort by Signal, Name, or Open First. There is a button to auto update (the update interval is set in the settings), and a button to update now. Like the others this has a popup that asks you to enable wifi if it isn't active and the exit selection from the menu is "Exit and Disable WiFi".
I like WiFi Analyzer best. It seems to have everything that the others have plus more. What's even better are all the settings it has to make things easier. The export feature is handy as is the screen capture feature.