Should you attend the most selective school? Maybe not:
Students who attended more selective colleges do not earn more than other students who were accepted and rejected by comparable schools but attended less selective colleges. (Dale and Krueger, Estimating the payoff to attending a more selective college, 1999).
Should you present papers in the conference with the lowest acceptance rate? Looking at this plot, there seems to be little correlation between acceptance rate and impact factor:
(Source: Sylvain Hallé’s blog.)
Conclusion: The best schools or the best conferences may not be those with low acceptance rates.