As I've said in another thread, with vote to save, the most popular HM wins. With vote to evict, the least hated wins, quite often someone hiding under the radar. Ben, Peter and Trevor didn't win for being the most popular. If a HM is divisive, both loved and hated by viewers, then hatred wins in a vote to evict such as with Sara-Marie. If that first season had vote to save instead, then she would have won. Also the season 5 results may have been different; I don't think the twins would have won.
There have often been complaints about little-known HMs winning and popular ones being kicked off. Vote to save therefore generally produces more satisfying results for the viewers. However, it can be argued that a HM who is hated as well as loved doesn't necessarily deserve the win. If Sara-Marie had won first season, or Paul in season 4, a lot of viewers would have been angry at the show and turned off in disgust. Therefore, perhaps both the vote to save and evict combo is the ideal, but the current system of vote to save is still better than vote to evict.