It used to be cheaper to go with travel agents because they had special connections with the airlines and could find you secret deals they didn’t post online. So, for many years, I would check fares online, then call a travel agent, and sure enough, the travel agent would have a much better fare.
Now that the internet has gotten so popular and travel websites have evolved, it seems to be a better deal to find your own fares on the internet because the secret low fares now seem to be published online. The travel agent generally charges a fee or a commission, so doing it yourself eliminates this extra charge.
Now, I usually have to book one international flight a year and I’ve become pretty darn good at finding cheap fares over the years. I’m pretty jazzed that the online airfare sites have evolved in a positive way that makes it much easier than previously, to find the best deal.
I have never used Priceline for airline tickets and I don’t know anyone who has, so I can’t comment on that. Their format before kept me from investigating further, but they may have changed things since.
You can use a site like FareCompare.com to compare multiple sites at once, which is very handy. In addition, I highly recommend signing up for fare alerts at any site you can, one that I use is TripAdvisor. You can sign up to be notified when fares drop from a certain airport (and if you have multiple airports in your area, I would sign up for all of them).
Play with your dates. Some days of the week are more expensive to fly than others (Tue-Thur is generally the cheapest), not to mention different times of the year (peak holidays). I find that generally you get much better deals if you book well in advance, but if it’s a flexible thing, you may just want to sign up for fare alerts and nab a cheap ticket when it comes up.