Google's unfair competition really shows in the travel niche.
Since google itself is an affiliate with most travel programs, they list tripadvisor and expedia tops, AND google's own affiliate traffic on sites it makes $$$ from.
If you go into travel, google is your #1 competitor.
Having said that, there are great affiliate programs including booking.com which is owned by expedia and I don't know how they're doing lately, but travelnow.com also wasn't bad. All these programs are owned by the same people, orbitz or something like that, so don't expect any real market competition in travel, it's the most monopolistic niche of all with google and a couple of companies controlling everything.