Comment by lisper

I mostly agree with this, but with two exceptions. First, I've had surprisingly good experiences with booking.com (no affiliation, just a satisfied user). And second, if you're booking a cruise, it's actually better to book through an agent. The cruise lines all have deals with agencies that forbid the cruise lines from undercutting the agents. If you find the right agent, they will give you kickbacks on their commissions so you actually end up paying less than you would booking direct.