Pru Orpington is fine, but it seems if you have any issues which lead to a required ELCS (placenta previa for example) then they WON'T LET you go to Pru (happening to a friend of mine right now).
The healthcare around here is a shambles for maternity since they closed Queen Mary Sidcup.
Therefore, whichever hospital you choose is going to be rammed !
I had DC1 at QM Sidcup. I had DC2 at Darenth in Dartford. Both were great.
Now though, if I go for DC3, I am not allowed to cross border to Darenth (probably because they closed Maidstone so Darenth is even busier as well)
I honestly believe that not one of them is better than another. It is totally pot luck on how many babies decide to come the same time as yours and how busy that particular hospital is on any one day. I think all Midwives are good, but there just simply aren't enough of them.
I would advise looking into your life and patterns - where can you get to for ante natal appointments? Is there parking? (not at Kings particularly!!)
If by train, what is access like? (Kings station is a nightmare right now and more steps than a pregnant woman should face)
Does a midwife visit your GP surgery? Can you see one there and still be booked into Kings?
Personally, I wouldn't go to Kings for the parking alone! You could spend £200 just giving birth. If a section, then probably more! That's if OH can find a space 
Also, if you went into labour at 9am, getting from SE3 to Kings whilst having contractions would not be fun! I have to say, travelling from SE3 to Pru Orpington is similar. There is a rail bridge closed at mo for a year. Traffic is horrendous even outside peak times.
In your shoes, I would choose between the two closest.
QE or Lewisham.
I think I would choose Lewisham
a) closer
b) have heard less 'it was crap' stories there than QE.
On a plus for QE, most of Sidcup lovely staff got transferred there....
You know, you could have all your ante natal at Sidcup including scans and all midwife appointments. Just not the giving birth bit (f'ing shambles)
sorry so long!