Ripley was just a space truck driver. True. Of course, Sarah was just an overworked waitress at a dinner. Both woman begin as rather ordinary individuals before events send them into heroine territory. Sarah's training accumulates mostly off-screen from different individuals. All the while she's safe as can be, on earth, waiting on that next Terminator attack. And the addition of both Reese and the T-800 protecting her goes without saying.
Ripley on the other hand learned the hard way. Ultimately alone, drifting from one dangerous location to another in the ass end of space. She learned to survive almost solely on her own, hands on, backed up against a wall, time and time again. She even had the balls to rescue both her worthless cat and Newt, the latter right out from under the Queen Alien's nose in the heart of the bug hive. Courage and a mothership instinct at it's very finest. She's also repeatedly impervious to the vacuum of space. Let's see Connor pull that one off.
However, to be fair, both women devoted the remaining years of their lives fighting their respective enemies. But Sarah just passed the burden on to her son and then died before Judgment Day hit. Ripley truly comes out ahead here, by finishing the job in making the ultimate sacrifice. She eradicated the enemy race, just as she had set out to do all along.
Then she did it again, as a clone. But I like to forget that movie happened.