Outland for an American applicant is generally much better. It is faster, for one thing - usually the applicant will get his or her PR within a year.
The PR the applicant gets will usually have Condition 51 on it: this just means that the couple must live together for two years after the applicant becomes a PR. If they break up before then, the PR could be revoked. The person is still a PR during this two-year period - they have the rights of any other PR; for example, they can work, apply for any job a Canadian citizen can (except for a few governmental jobs that require security clearances), can get health care just like a citizen, etc. After the two-year period is up, the person no loonger has this condition attached. If the couple breaks up then, the PR remains a PR and it cannot be revoked for that reason.
So after applying to sponsor outland, the application process might take 4 months to a year. Once it is done and the applicant has a PR visa, he or she enters Canada using this visa and becomes a PR.
If they have applied inland, and have included an application for a work permit, the work permit will usually be awarded about 4 months later. Then the applicant can work, but they are not yet a PR. The processing will continue, and after another year or more they will get their PR visa. They make a landing appointment, and then the person becomes a PR. It can still have conditions on it.
The thing to realize is that for an American, they might get their PR visa in 4 months if they apply outland - usually a bit longer, but it could be that soon. If they apply inland, they might get a work permit after 4 months, but they are still a long way from being a PR. So for most cases, an applicant who applies outland could be a PR and working in not much more time than it would take for the inland applicant just to get a work permit.