A few days ago, I was asked to trim the hedges at a neighbor's house. I used my straight trimmer and it took me less than 20 minutes to trim down the bush. When I used my curved trimmer, it took me more than an hour because it got stuck in the branches of the hedge.
I think that a straight trimmer is better because it doesn't get stuck in foliage and therefore saves time as well as energy on using a curved one for every hedge.