As much as I love sleeping under the stars in the High Sierra in Summertime, I also enjoy staying warm, dry, and free from mosquito bites. I am therefore a big fan of Black Diamond's single-wall tents, which remain the lightest ‘real’ tents available—freestanding, breathable, highly water-resistant shelters that shine in most conditions.
The smallest of the bunch is the solo 2 lb 5 oz (tent & poles) Oneshot. Initially the OneShot didn't make a lot of sense to me. I thought it was a bit cramped, and too close in weight to Black Diamond's two-man Firstlight tent. But I've reconsidered. If weight is a critical consideration, maybe the Oneshot makes sense after all.
The 2 lb 11.5 oz Firstlight is the original, first-generation Epic™ tent, and compared to its more refined siblings, it is a little primitive. Soloists will find the Firstlight quite roomy, but partner up and things get real cozy real fast. Ventilation can be a problem with the Firstlight, and the interior feels a bit claustrophobic as well.
I really like Black Diamond's HiLight tent. The two-man HiLight is almost identical in size to the FirstLight, but it feels much roomier: a cross-pole awning and trapezoidal floor open up the view and the ventilation. This is a sharp, airy design that considerably improves upon the features of the Firstlight. Note, however, that while the HiLight is supposed to be lighter than the FirstLight, my scale says it is two ounces heavier, at 2 lbs 13.5 oz.
The largest tent in this roundup is the 3 lb 3 ounce Lighthouse. The Lighthouse is a two man tent for climbers who don't want to rub shoulders all night. Taller hikers will appreciate the tent's extra length and breadth. The design is identical to the Hilight, but with a big 87 x 51" floor for extra room. And look at that weight: just barely over three pounds!
If you're new to Black Diamond's tents, they can be tricky to set up at first. Be especially careful not to puncture the tent body or floor with the poles! As you gain experience, this becomes much easier. Each of these tents will do 4-season duty if needed. As always, choose protected camp sites and be realistic in your expectations. To add room for cooking or extra gear, you can purchase optional vestibules for each tent. The vestibules add about a pound to the total weight, however, which pushes into the double-wall tent range (and makes the single-wall's upside less appealing).
Perhaps the greatest concern with Black Diamond's single-wall tents is their Epic™ fabric, which is listed as "highly water-resistant" rather than waterproof. For more on that subject, see Epic tents in rain. For experienced backpackers, I don't hesitate to recommend using Black Diamond's ultralight tents in Alpine environments, including rain and snow. So long as the wet weather doesn't go apocalyptic on you, I think these are the finest lightweight shelters you can buy.