Dynamite Dean
Depends on the type of aircraft you want to fly.....
SAC has C150's/C152's and C172 plus Slingsby T67 Firefly for aeros. Phoenix have C150's and a Beagle Pup.
Yes, Phoenix are a bit cheaper but, as big al says, you won't have access to the great clubhouse/restaurant.
If you want to come and have a look around at Nethers I'll glady introduce you to both Sheffield Aero Club and Phoenix people.
For your ref:
Sheffield Aero Club
Phoenix Flying School
Camaro