Grunt VS Gulp: Less compile and autoprefix

gruntfile.js

grunt.initConfig({
   less: {
      development: {
         files: {
            "build/tmp/app.css": "assets/app.less"
         }
      }
   },

   autoprefixer: {
      options: {
         browsers: ['last 2 version', 'ie 8', 'ie 9']
      },
      multiple_files: {
         expand: true,
         flatten: true,
         src: 'build/tmp/app.css',
         dest: 'build/'
      }
   }
});

grunt.loadNpmTasks('grunt-contrib-less');
grunt.loadNpmTasks('grunt-autoprefixer');

grunt.registerTask('css', ['less', 'autoprefixer']);

gulpfile.js

var gulp = require('gulp'),
   less = require('gulp-less'),
   autoprefix = require('gulp-autoprefixer');

gulp.task('css', function () {
   gulp.src('assets/app.less')
      .pipe(less())
      .pipe(autoprefix('last 2 version', 'ie 8', 'ie 9'))
      .pipe(gulp.dest('build'));
});