I have an Ergo & a Patapum Toddler. My DS is 16 months, 26+ pounds, 32+ inches (mostly torso) and I am large framed. We have used the Ergo since he was 7 months (that's when I bought it used off ebay) and we love it! I almost always throw it in the cart when we go shopping (if I don't I usually wish I had) so that if he gets cranky I can put him in the carrier & he calms right down. I have just recently started using the back carry & it is extremely comfortable (except when he decides that it is fun to pull mommy's hair) but takes a little practice to get him positioned. I got the Patapum toddler (used off ebay, as well) because he is all torso & I anticipate using the Patapum more as he gets bigger.
This link has a comparison of a bunch of carriers & includes the size of the carrying person as a basis for camparison:
http://www.theportablebaby.com/carrierfeatures.html