Seeing as there are more 'new' (16) A320s than 'old' ones (11), if your flight is listed as '320' you are more likely to get a socket than not.

However, there seems to be no rhyme or reason to the new/old deployment. Our early morning flight last Thursday for instance was an old 320 (that went tech in the end!) but the midmorning and lunchtime departures were new 320s (in fact, the same aircraft).

As they say, YMMV.