As far as only easiest, if I know an airline serves a specific route I'll go to their website and book.

If I'm price shopping or I don't know who serves a route I'll go to Kayak or Google Flights and look at my options. When I find a flight I like I'll go to that airline's website and book there.

I never use the Orbitz/Expedias etc. they're ok until you have an issue, then it's "Not my problem. Call someone else."