I carried a G27 for about 6 months and considered both of your options and tried one.
I carried iwb with a kholster (the same idea as the supertuck). Not bad, but it gave me a back ache having the gun in the 4-5 position.
I thought I'd like to try a shoulder rig, but then sold my G27 and now I pocket carry a P3AT.
If you go shoulder holster, try this for faster weapon retrieval...
1. remove your button and sew them on the outside of your shirt over your button holes
2. sew velcro on the inside of your shirt in place of the buttons you removed
Now all you have to do is pull the shirt open with your weak hand and draw the gun with the strong hand.