If I make tacos at home, I use the hard shells for myself. Sometimes, if it's a chicken taco I made at home, I will use the soft.
If I'm ordering from Taco Bell, I get hard if it's beef. If chicken, I get soft.
If I'm at Chipotle I always get the 3 soft tacos chicken. Usually this is because I will eat 2 of them and save the third. With the hard well... they get realllllly gross (read: mushy and just off) if you save it.
If I'm ordering from someplace with real Mexican food or a taqueria, I will get soft (or however they make them), if I'm getting tacos.