Disclaimer: I am an agent that works with several active investors besides my own investments.
Like most things in life "it depends" If you have an average residential agent that is not used to working with investors then I am not sure how much better than the discount or flat rate route they are.
However, if you can find a great agent he or she will become a member of your team and will be worth every penny to your business. A great agent for an investor is not necessarily the team with the biggest advertising budget. For an investor the best agent will be the one that totally understands your criteria and style, that instinctively knows if a deal is worth bringing to you and understands how important a short time on market is to your profit margin.
This agent is not always easy to find. You are looking not only for a certain skill set but also, to some degree, a personality match.
Sometimes trial and error is the only way to find this component of your business.
Best of luck.