In a real quandry, would love to do aerodrome but it seems a complete lottery as to whether i'd be fortunate enough to get the app training (or unfortunate enough depending on your view)
Postings and streamings are always a lottery with NATS
More seriously though, towards the end of my Aerodrome course we were all asked whether we would prefer a London posting or do the approach course. It ended up being a 50/50 split between the courses, and nearly everyone got what they asked for. Ok; we were perhaps very lucky, but sometimes you have at least the oppurtunity to give them an idea where you're coming from.
As regards to whether to choose Area/Aerodrome, well its been done to death, and without going into it, the general consensus seems to be that people love whichever discipline they end up in.
If Approach radar is what you want to do long term, then Aerodrome is a good choice. Even if you ended up going to a London TWR, they are all great tower units in their own way and you'll have a great time and get great experience. There will then always be the oppurtunity at some point to move on, and do the radar course. Or you could end up at a unit that has both TWR/APP "both of best worlds" and there are the Approach only postings (Aberdeen offshore and London TC). As stated above, the college tend to know TC requirments a while in advance.