Kim, they're both two entirely different kettles of fish. Neither is better, they are both good for different things. Some pros/cons of both:

Ergo: two shouldered SSC (soft structured carrier), good for heavier babies/toddlers and long carries, needs infant insert for newborn, reasonably quick to put on (compared to a wrap for example), quite bulky though, they don't fold up into a handbag or nappy bag. Not particularly attractive either, utilitarian rather than aesthetically pleasing. Best for back carries. Can't be used for reclining (cradle) positions. Good accessories - toy ring, pocket, optional front pouch and backpack. Weight is supported on the hips rather than the waist (like in a mei-tai). Although most people love them, some people (myself included) find that the shoulder padding on the Ergo is quite bulky, and that the angle of the shoulders does not suit narrow shouldered people. I personally find other SSCs to be more comfortable than the Ergo, but for most people, the Ergo is a really good, comfortable and supportive carrier.

Peanut shell: I have not used a pouch, so can only give general pros and cons. Convenient, quick and easy to put on and to travel with (folds up small), must be fitted to the wearer and not adjustable. Pretty though. One shouldered carriers are not as supportive for long carries, heavier / older babies and may not be good for people with back or shoulder issues as they carry the weight unevenly. However, great for shopping and quick up and down trips.

HTH!