Highlighting achievements is a good thing. The conference can signal which papers it considers very good, and authors can take deserved credit. ECRTS moved from single Best paper only to a number Outstanding papers to serve these goals better.
In my experience, there is rarely a single best paper, clearly above all others. Typically there is a small group of very good papers, and the decision which is the best is often a consequence of the criteria used, rather than authors’ achievement only.
Candidates for best papers are typically nominated during the evaluation process, the actual decision often taken at the conference, i.e., after the proceedings have been completed.
At ECRTS, we introduced Outstanding Papers, a small number of very good papers, decided upon at the TPC meeting. This allows including them in the proceedings, and makes the awards visible with the papers after the conference. So, more authors get credit with higher visibility.
For the actual best paper, we formed a very small committee to decide during the conference, taking presentations into account. It included the technical program committee chair their for knowledge of papers, technical committee chair as best paper also represents goals of the conference.
We put the outstanding papers in a special session of the program for added visibility (and put it at the end of the conference to counter attendance erosion). Making the awards visible via conference web site etc, is an easy way to support authors and community.