Pheonix is much cheaper, something like £64 per hour (wet) for their C150s and no membership fees to pay. I used to rent from them about 18 months ago.
I think SAC charge around £75 (ish) for 150/152s and about £95 (ish) for a PA28/C172. I'm not a member so can't vouch for current prices but these numbers were about what they quoted when I enquired some six months ago. SAC also has membership fees of something like £150 per year for flying membership, but this does give access to their excellent club house and if the social side is important to you, then you'll probably find SAC a good choice.