Compare the 644 Tents on Ten Pound Backpack based on their weight, price and a few more features as well.
When you go as big as a 6 man tent, you can pretty much throw the idea of lightweight backpacking out the window. The one exception to that might be using a tarp, but with tents, you are looking at 15 pounds of tent, give or take a few pounds depending on the specific model.
6 Man Tent
Here is what to look for in a six man tent.
Ventilation - With 6 people sleeping in one small space, ventilation is going to be one of your biggest issues. With that in mind, you should be looking for a tent that has good ventilation, so that you can be reasonably sure you're not going to wake up soaked in condensation in the morning.
Extra Space - People tend to like to bring a few things, like a flashlight or a few pieces of warming clothing, in to the tent with them, if not more gear. When it's just you or you and one other person this isn't such a big deal, but all those extras for 6 people adds up. Try to find a tent with some storage areas on the sides of the tent, or at least some extra space, so that you're not crammed in like sardines.
Best 6 Man Tent
Here are a few of the best 6 man tents.
Marmot Halo 6 - Based on reviews, this seems to be the most popular 6 man tent currently on the market. First, it has two separate doors, which does nothing to keep weight down, but does make it so you don't have to go crawling all over other people if you have to get up during the night. It also has adjustable side ventilation and gear storage pockets on the walls. The abundance of features, however, means that you have 18 pounds 15 ounces, or 8.59 kilograms of tent to carry around. Fine if you are car camping, but perhaps not the best option for backpackers.
Kelty Trail Ridge 6 - The great thing about this tent is the weight. For a 6 man tent it is actually reasonably light, at 13 pounds 13 ounces, or 6.26 kilograms. Beyond that, the Trail Ridge 6 has two doors, for easier entry and exit, and storage to make sure that there isn't a whole mess of gear on the floor. One additional feature worth mentioning is noiseless zippers, so you don't have to worry about waking everyone up with your midnight trip to the bathroom.
REI Kingdom 6 - The main thing that stands out about the Kingdom 6 is that is has a separator wall that can be zipped down, to turn the 6 man tent in to a 2 room tent. The separator wall increases the wall storage space available, and the 2 doors mean that you you don't have to worry about going through the separator wall during the night. It does weigh 17 pounds 3 ounces, or 7.8 kilograms, so again a tent better suited for car camping.