My advice - opposite sexes with bully breeds.
I have a SBT female and a x breed female. The SBT is a lot bossier with females then males. No major probs, and the combo works for me but if i was ever to get another Stafford it would be male.
In my opinoin a french bulldog and an Amstaff are not very suited. Different needs, diff exercise levels, Not impossible but imagine this. Warm day, amstaff happy to run at the doggy park for an hour. F bulldog is buggered after 15 mins, puffing and panting. It's little things like this that could annoy you and your dogs after a while, possibly cause jealousy between the 2 , but do as much research as you can about the breed, talk to breeders, owners and make your decision then.
In re. to females not being stocky enough...Do you really want to make a decision based on the perfect amount of muscle?Seriously!
I've seen some tiny males and huge females, shorter, taller, big heads, small heads.... They all vary. You can always request the biggest female of the litter.