Speed

• You'll need to walk around your lawn while hovering the cutting head about 2 inches above the ground. The easier you can walk, the quicker you can trim and the faster you can move on to other things. Straight-shaft trimmers allow you to walk quickly in a straight line, as your view of the head in front of you is unobstructed. This allows you to see ahead of your cut and move the head into proper position. Straight-shaft trimmers work well on long straight areas like your driveway, sidewalks and fence lines. Curved shaft trimmers allow you to operate with speed in areas that require more maneuverability, like corners or tight areas.
  
  

Maneuverability

• A curved-shaft trimmer keeps the head of the trimmer closer to your body, so if you have to get in close to trim around bushes, flowerbeds or between rocks or other obstacles, you'll be able to see the head better. The curved shaft will also allow you to move back and forth and in between these areas much quicker since you can see the head better and it's closer to your body. Straight-shaft trimmers also have maneuverability around these areas, but they may put more strain on your body, require more foot work and may not be as easy to see.
  
  

Level of Comfort

• The most important advantage of a curved- or straight-shaft trimmer is the level of comfort it provides you while working. These trimmers, with full gas tanks, can weigh more than 10 lbs., which can add up over the course of three or four hours of cutting. With curved-shaft trimmers you'll be able to keep it closer to your body, so it may put less strain on your lower back. A straight-shaft trimmer will allow you to speed through certain areas, which will reduce the overall trimming time. Most importantly, you should test these shafts while at the store by walking and moving the trimmer around.
  
  

Considerations

• Whatever shaft you decide on, it needs to make the job better and easier, which will really come down to personal preference. Both cost about the same, both can get damaged in the same way and both require the same amount of maintenance and repair. For these reasons you should choose the string trimmer style that you feel more comfortable holding and moving around.