My GPA, if I work hard senior year, could probably go up to a 3.93 unweighted, while with only my grades until junior year, would be a 3.87.
Which one would colleges consider?
Many colleges, including the majority of public universities, decide regular admission based on grades through junior year. Many others, including most of your higher ranked private universities, require submission of first semester senior year grades after you have applied and use those along with junior and before grades to make the decision. Thus, whether any senior year grades will be used depends on the particular colleges you apply to.
Note that many of those colleges that require and consider first semester senior year grades for regular admission have early decision or early action programs where you can apply and get a decison early, most often mid-December, and for that grades through junior year are used. Also, all reserve the right to withdraw any admission given if your final transcript after senior year shows you have done poorly senior year.