To show the difference in sound quality, the salesman contrasted the latest model with last year's.
To show the difference in sound quality, the salesman contrasted the latest model over last year's.
To show the difference in sound quality, the salesman contrasted the latest model with last year's.
To show the difference in sound quality, the salesman contrasted the latest model over last year's.
The verb "contrast" idiomatically takes the preposition "with": "to contrast P with Q." All other prepositions are incorrect.