On Patapum versus Ergo, they really are very similar in terms of how they are used, how to load your child, etc. Note that I only used them for the back carry, not any other position, so I can't speak to how it wears as a front carrier, etc.
The Ergo does have more bells and whistles, but they weren't things I was very likely to use (like the sleep hood, which was useless for me as my toddler son won't sleep in carriers any more). I did get the small waist sack attachment for the Patapum, as it is nice to have a place to put $ & keys. If there was an attachable day pack available for the Patapum (as there is for the Ergo) I might consider getting one.
The clincher for me was fit. I am definitely plus-sized (broad shoulders and chest), and I just felt too squeezed in the Ergo. It was very uncomfortable over the shoulders and under the arms/beside the breasts. The Patapum, on the other hand, is extremely comfortable for me. It is slightly less padded, which I think helps make it feel less constricting (I suppose the lesser padding could be a downside for some, though). I also found it easier to tighten the straps on the Patapum. My son seemed equally comfortable in the Ergo and the Patapum.
Oh, and last but not least: the Patapum costs less!
Hope this helps!
