Sigmoid colon with penile inversion is much more invasive than just penile inversion. Penile inversion techniques requires a commitment from your side to daily dilate twice or thrice almost every day life long. I would say it would be a preferred technique in case you are not concerned about the depth and about the fact that the vaginal opening in this technique can eventually close if you do not do your dilations on a regular basis. These are basically the cons of a penile inversion technique.
Although sigmoid colon with penile inversion solves these, it comes with its own set of cons - I now have a visible scar in my stomach (which I hope it will fade away), my tummy is now swollen and comes out (there is a bulge), which again I hope gets to shape with time, affects your bowel movement and takes time to get to shape.
So it really depends on you. Though AnuLuna, if depth is not a prob, I would suggest only penile inversion technique.