[lucaspiller]

Usually I search with an aggregator find the cheapest carrier, then book directly with that carrier. I've found booking sites to be a bit hit and miss - often they add extra booking fees that make the chosen flight more expensive or you miss out on certain options. In Europe I usually use a combination of Momondo, Skyscanner and Kiwi (formerly Skypicker).

[colinbartlett]

The aggregators are also always showing the cheapest fares, regardless of the restrictions on those fares. More and more airlines have fares like Delta's "Basic Economy" which does not even let you pick a seat. Everyone is familiar with the long standing "non refundable" restriction on most of these fares but the newer restrictions vary from airline to airline and the aggregators don't do a good job of detailing those.

Contrast that to booking on most airline sites where they very clearly and very obviously show you the restrictions because they publish the fare alongside of the less restrictive fares as a way to up sell.