While frequently asked, this is a difficult question. Booking directly with an outfitter and booking an outfitted adventure through an agent each comes with advantages and disadvantages. Let's run through the pros and cons of each.
Booking directly with an outfitter allows you to know whom you are dealing with right up front so you can begin the all-important communication immediately. You can ask questions directly and immediately of the man or woman with whom you'll be entrusting your business and your pleasure ... in fact, BEFORE you book the hunt.
The biggest drawback to booking directly with an outfitter is you aren't getting the endorsement or assurances of a reputable booking agent who has thoroughly vetted the operations for which he/she books. Good booking agents always personally check out every outfitter for whom they book.
Though www.OutfittersRating.com is a great source to check out the ratings and reputability of outfitters, it is only one source of many you should investigate. An experienced, reputable booking agent will only direct you to outfitters he/she is certain will provide you what's promised. Unfortunately, not all booking agencies are reputable; some are just in it for the quick buck ... just like some outfitters.
The biggest drawback to booking through most agencies, is they won't tell you the precise location, outfitter or camp you'll be hunting with until AFTER you've paid that first deposit. This is simply to avoid the business end-around of the agent making a recommendation, then the hunter going directly to the same outfitter to book the hunt directly, and, potentially, negotiating for a less expensive hunt.
Hunters may wonder how booking agents make their money, especially when they see hunts booked through an agent going for the same price as hunts booked directly with the outfitter. Outfitters tend to view booking agents as an advertising resource. For example, if a booking agent is working a series or sport shows, or operates a vigorous website, then the outfitter doesn't have to commit time or financial resources to those kinds of promotion. So if advertising costs are, say, 15% of a hunt and the outfitter doesn't have to spend that money directly, he can afford to pay that amount (or perhaps even less) to the booking agent for finding hunters instead.
So part of the decision between booking through an agent and booking directly with an outfitter comes down to you and your approach to your outfitted hunting adventures. If you have limited time to commit to research and negotiation, then you'll want to consider a booking agent. You can simply say, "I want to hunt mule deer in Alberta" or "I want to hunt plains game plus cape buffalo in Africa" and the booking agent will come back to you with multiple options, albeit without telling you exactly the operations you're considering.
But if you're the kind of hunter who wants to be in control of every aspect of the research and negotiation from start to finish, then working the sport shows or the internet, coming up with your own options, and diving in to book directly with an outfitter will be more to your liking.
Another advantage of booking through an agent, especially some of the larger operations, is that they can handle travel and accommodation arrangement as well. They are really full-service travel agencies specializing in hunting and fishing adventures.
If you go the route of booking through an agency, one of the questions on your list should definitely be, "How do the operations you're recommending rate on www.OutfittersRating.com?" If they are not in the program, there may be a reason!