I have been using a Aker White Lightning or Classic 3 Slot open top (I've had it for a while and can't remember) for IDPA, as I live in a state that isn't that gun friendly for a CCW, using a Commander size 1911. I do have a light shirt that I wear over it. I did have a Galco similar to the 3 slot (?Pancake/FLETCH?) but the thumb snap was designed that the hammer had to be down. The Aker I can carry C&L'd. I have been looking at getting a Blade-Tech UCH IWB for it in the future. The last IWB I had for it (don't remember mfgr/model) really didn't stay where I wanted it but it did hide most of the gun and the frame sat in a good spot to hide the rest with an untucked shirt.
I'm always weary of shoulder rigs. I just don't like that I'm always pointing my weapon in the wrong direction while trying to get it out, mainly at MY arm. Additionally it is nearly impossible to secure if the "baddy" wants to get your weapon. A belt holster you can leverage your arm against the gun to keep it in place while a shoulder rig you can only clamp your arm down, not enough to keep a determined opponent from getting it.