Summary
We reviewed some of the potential settings in the inner and outer solar system and you may have noticed something. For both Mars and Venus, the assumption for life is that it most likely arose a long time ago, when both planets had more Earth-like environments. We expect any life on those worlds to be the hardy survivors that are managing to hang on.
By contrast, the sub-surface ocean settings of the icy satellites and even the hydrocarbon surface of Titan are active and relatively stable environments. It clearly took considerable time for these settings to develop, but they have likely been stable for much of the history of the solar system.
Nobody knows if or when we will find evidence of life within the solar system. While icy satellites may arguably be the best setting, the next missions to them will not arrive for more than a decade. By contrast there are multiple missions to Mars in various stages of progress. This likely means that if extraterrestrial life exists in the solar system, there is a good chance that we will find it on Mars first.