That is pretty interesting. Amount of code for both projects is vastly different.

XEL: http://imgur.com/iMZIXyf
      - Code for the XEL miner
 

SONM: http://imgur.com/noS8lzI
      - Code for core includes miner and more.
  
           http://imgur.com/TxXlNL3
      - Code for their The-Factory project where all their smart contracts are located.


Circulation is another thing to look at though and:

XEL - has 86,023,008 XEL circulation w/ a max of 100,0000 XEL
SONM - has 331,360,000 SNM w/ a max of 444,000,000 SONM