Better to book through tour sites or attraction website?

I'm speaking in generalities, but for most major sights, the really long line is the one for people who need to buy tickets. The line for people with tickets is always shorter. If you can negotiate the website and buy tickets there, that's the thing to do.

With "skip the line" options, you will still be in the "skip the line" line.

I avoid paying more for nothing ( or next to nothing) extra to 3rd party sites whenever possible. A ticket is a ticket- whether bought from the official site or a 3rd party. A VERY little research on your part will enable you to navigate the entrance process. easily on your own.

I almost always book directly through an attraction's own website or official ticketing vendor. Once in awhile we'll buy a tourist pass if it covers enough of the attractions we wish to see and we have time to do them. For instance, we bought the Paris Museum Pass for our week in the city, and just purchased individual tickets for a few things it didn't cover. That pass comes in 2, 4 and 6-day values.

I figure there's no need to benefit a third party when I can do it more inexpensively on my own.

Viator may be a "3rd party site" but I've used them several times and been very pleased with every tour. The key is to research your options and decide where you want to spend your time and money. Compare to other sites. When I've used Viator, their prices were consistent with other tour websites- and yes, usually a tour is much more enjoyable when you don't have to worry about transportation or when you have the expertise of a guide. When I go to Versailles next month, I ordered directly through the Versailles website for a self guided tour using a headset provided by them. When I went to the catacombs two years ago, I bought skip the line tickets, but still had to wait in line for nearly two hours (while the non- skip the line people were waiting more than double that). Usually skip the line passes get you directly in a special entrance. As for the Eiffel, I booked those through the Eiffel website the day they became available. If you're too late to do that, then you have to decide whether it's worth the splurge to pay one of the 3rd party sites. Always compare if you can, so you're getting the most bang for your buck. I've used Viator in Scotland, Holland, Russia, England, France and Germany, as well as in the US. I've enjoyed every tour with them. In the 2 cases where I was disappointed (neither the fault of Viator) they refunded my money quickly and without hassle. In my opinion they're almost always worth the extra cost. You didn't spend thousands to go to Europe just to wait in line for hours and hours, or to (necessarily) wander around a spectacular site, lost. Do what works for you. Have fun!
Lisa

Viator is a re-seller of other peoples tours. That same ticket you bought from them, is being offered somewhere else by a tour company. They are paying Viator a 25% commission to sell their tickets. Look online, especially on Trip Advisor which has the most listings, to see if you can find this same deal from the original company.

If you are reasonably healthy consider walking from the ground level to the second level and catching the elevator from there. We did it with our kids ages 8 & 10 at the time. It was a lot of fun and really didn't take that much time. You can go at your own pace.

Always book directly with the site. Why add another layer of expense?