I am a member of Fitness First and was a member of California Fitness before.
This is what I think.
1. Both are out to get as much membership sales as possible. After you join, they will then try to get you to sign up with a personal trainer. A session with a personal trainer works out at between $75 to $100 depending on how much they suck you in for.
2. Gym classes like yoga, dance, aerobics are about the same for both.
3. "Good" things about FF over California.
a) The smaller locations will give you towel, t shirt and shorts to use for gym. You cant keep them of course- you hand in your membership card while u wear the stuff and get it back when u return your locker key.
b) FF provide lockers with locks. At California, you have to provide your own padlocks. If you forget, you can buy one for $5.00. I personally hate this. I have bought 3 padlocks from them because of this.
c) Bathrooms are quite nice. Marble, carpet, deoderant, talcom powder, soap.
d) Provide drinks and cups- you get it from a dispensor like u see from McDonalds and BK. Is "free".
e) Some FF places like Capital Towers opp Tanjong Pagar have swimming pool too. The shorts provided can be used as swimmers I think.
f) Can hire movies on VCD at no charge once you are member. From memory, they have quite a range, though it isnt kept up to the minute.
4. "Good" things about California over FF.
a) Seem to have larger gyms, so more room and equipment.
b) Opening times seem to be slightly longer- ie the close later.
c) The cardio machines, like treadmill and stationary bicycle, have built in fans which you can point at your face to cool you down. FF ones dont. I like the fans.
But regardless which gym you choose, the main thing is to know how to use the machines there and be disciplined.
If you dont, then it is a waste of time.
They offer a free one session with fitness trainer. If you are new to the machines, then you wont believe how much you dont know about using them.
Just dont get sucked in unless you really want to get a trainer too.
I hope this helps

Cheers!