In a 3 footer you have some options. There are a few mbuna (labs, rusty's, Saulosi), many tanganyikans, and a number of new worlds. In the smaller tank you're looking at a pair of kribs, rams, or perhaps some shelldwellers.
Providing your filteration is very good. You can get away with 3-4 fish in a 70litre.These fish are used to crouded condition, making caves should keep them happy.Stick to Labs or solusi or other small fish.It's always better to use the biggest tank you can get.You might wanna try dwarf cichlid's.
In a 4ft tank your range will be better of course.You can go for lombardoi,bumble bee's, johannii,Afra... Check this page out it will give your an idea.Also keep in mind the most cichlid's can get to very large size's, like 30-40cm which will mean if you need to stick to some smaller growing fish or else you will need a tank change 1-2 years down the track. B)