Which is the best site to book airtravels
 

Please in your opinion which is the best airflight company in Europe for online bookings?

What you are referring to is an 'OTA' - Online Travel Agency - in FlyerTalk speak. There's a ton of those out there, and they all have their strong and weak points. Such a thing as "the best" one simply doesn't exist.
Check out the https://www.flyertalk.com/forum/onli...-agencies-204/ section right here on FT which will give you a good overview about the topic (and incidentally, where you should have opened this thread in. I have alerted a moderator to move your question there).
Myself, I usually use tools like ITA matrix, google flights , Hipmunk, skyscanner or Kayak for pricing information and research, but book directly with the airline on the airline site.

moved......

For Europe travel also try Omega Flightstore and Skybooker. I've purchased tickets from both without any problems, plus they are IATA accredited.

Expedia, Booking I prefer mostly for Online bookings.

For round trip bookings, I recommend you always book with the airline direct. All the airlines now have pretty user friendly websites where you can pick your flights, class of travel and any add ons, like luggage, extra legroom seats, etc. And if you have any changes, it's so much easier to deal straight with the airline.

The one exception is if you are doing a multi city itinerary which may involve different airlines. Here, I have found sites like Expedia offering terrific deals and much cheaper than if you tried to book with the airline. Also very user friendly.

It depends on your origin and destination airport. One air carrier or OTA can offer you a cheap flight on one route but may not offer you the best deal on another. So it’s better to not make an opinion. Always do your research before booking a flight.

Both of these deal with Economy only?