I prefer Front squats to back squats, mainly because I have horrendously poor shoulder flexibility plus a history of RC impingements and back squatting simply doesn't agree with these two things!
As for Deadlifts vs. SLDL or RDL...well you can't really compare them because they're different exercises with different purposes. Conventional deads are a posterior chain exercise but they make much greater use of your back muscles than your legs, whereas SLDL and RDL place far greater emphasis on the hamstrings. Most people would use Deadlifts as part of their back workout, but SLDL or RDL as part of their leg workout.