Tools for measuring wireless strength in iPod Touch?
If you are talking dBm, which you will see most wifi scanning apps use, it is actually not that difficult to understand. Basically higher numbers are better, and even negative numbers actually represent positive quantities, just smaller ones. 

From the wikipedia entry on dBm:

Zero dBm equals one milliwatt. 
A 3 dB increase represents roughly doubling the power, which means that 3 dBm equals roughly 2 mW. 
For a 3 dB decrease, the power is reduced by about one half, making −3 dBm equal to about 0.5 milliwatt.

There is also a pretty dang useful chart.


−10 dBm Typical maximum received signal power (−10 to −30 dBm) of wireless network
−70 dBm Typical range (−60 to −80 dBm) of wireless received signal power over a network (802.11 variants)


Sorry for not answering the original question, but I think with this knowledge you will be able to powerfully determine the strongest source of transmissions.