From Drumcode to the Sonar Day events is just a few minutes, but also the night event is reachable with a short walk (half an hour?). Public transport in BCN is also very goods (buy the T10 ticket --> 10 rides for about 10€).
The Drumcode venue itself is amazing (Poble Espanyol), nevertheless the volume restriction at the main venue is quite annoying. I personally prefer the smaller floors, but they are hosted by Rush Hour & Detroit Love on this day. Last year the Innervisions event was fabulous (especially the smaller floors), I can recommend if you like this kind of music (there are also a few techno acts on the lineup like dettmann).
The "Off Events" at Poble Espanyol are also organized from the sonar team btw .