No brainer !
The fact of the matter is you will be paying Cabair a lot of money to sit around on the ground at Biggin Hill waiting for your turn to get onto the runway.
Biggin Hill is just to busy to make training a realistic option compaired to Stapleford.
No doubt you have been fed a bit of PA28 better/busy airport bull from Cabair, dont fall for it the C152 is a just fine as a training aircraft.
After thirty years in this business (and 10,000 hours) I know by reputation who is ripping new students off and who provides value for money training, the Stapleford Flight Center have a very good reputation and can take you all the way to the (F)ATPL , Firecrest will do you a good deal on PPL,IMC & Night.
Also I can recomend the British airways flying club & WLAC but being the "wrong" side of London these may not be an option due to the traveling involved.
A question to always ask a flying club is "What do do I actualy pay for an hours flying". If the answer is £** + VAT + landing fees + Instructor charge + a fee for not keeping your account in credit, then you are in the wrong place.