I'm not even going to get into the double vs single wall debate since that has been hashed out more times than Charlie Sheen has made an Ass of himself, but I'll just point out a few things for the sake of discussion:
Keep in mind that these comments are comparing traditional double wall tents, not necessarily the UL tarp and nettent combo that is effectively a double wall "tent."
"Double wall because of the option of going lighter if I need to by leaving the screen portion at home."
--single wall tents are inherently lighter to begin with. No need to leave parts behind. No parts to even leave behind!
"Double wall because it breathes better (less condensation) than a single wall."
--yes, condensation is something you have to think about less in a double wall. However, it's still there. With proper venting and pitching techniques, you can minimize condensation in single wall shelters. Now, if you leave that nice "screen portion" of your double wall tent at home to save weight, then you are right back to a single wall shelter anyways.
"Double wall because You have venting options when you do bring both parts with (and "windows")"
--Any single wall shelter worth it's weight (IMHO) has venting options built in, and often they have way more venting options than most double wall tents. Tarptent's Double Rainbow has two peak vents, the entire bottom perimeter is mesh so venting happens there too. You can also set up both "porches" for expansive views and venting, even in some pretty hard rain.
Now, winter and above treeline conditions are a whole 'nother story.....
There are some pretty nice lightweight double wall tents out there. For the weight and my camping conditions, I personally have no reason to go back to a double wall tent.
Ok....I guess I did get into the merits of double vs single anyways!