Not being a first author diminishes the contribution of co-authors? If a group of students (say, 3 students), produces a work which has been accepted to a reputable conference. All of them contributed equally to the project,from implementation to writing and proof reading of the paper. 
How should one decide who should be the first author. Even if the names are listed in alphabetical order, so by not being the first author, does it affect the prospects for the other two in any means ? 
My field of research is computer science.

(This question has been partly inspired by the  flurry of questions on ASE, regarding the importance of being the first author)
It depends on the subfield of computer science. For example, if the paper is in theoretical computer science, then author order is alphabetical, and the equal work put in by the authors is not negated by the author ordering. If in a discipline where author order is meaningful, then it's standard practice to (say) order the authors alphabetically and add a footnote saying that all authors contributed equally to the work.