I know it has been hashed out before, but things change... perspectives, technology, what gear is being made, etc.
I am sure I am not the only one that owns both a tarp/bivy combo and a hybrid tent. As a given, let's assume the need to protect against both rain and bugs. In my case, here is what I have to work with:
Zpacks hexamid solo tarp (Ti stakes, guy lines, stuff sack), ground sheet, Ti goat bivy -- 493g all in.
SMD Skyskape X, CF poles, Ti stakes, ground sheet -- 575g all in.
I have gone back and fourth on this issue many times. For years I was a tarp guy, then when I got into UL several years ago I started to get into tents again after seeing how light they had gotten. Then when I got into SUL I got back into tarps, and for the first time bivies. I then had second thoughts about bivies due to condensation and being tricky to get in and out of them. The condensation bothered me the most, but then I got the idea to mod my bivy and put a vapor vent in the foot box where I get the most of it. Now I am planning on going tarp/bivy this summer for my SUL trips, assuming this mod words out alright. Not only is it lower weight, but also gives me more options; the two big ones are cowboy camping bug free, and being able to use the bivy in trail shelters.
So for the time being, tarp/bivy wins out for me. In the future I want to upgrade my bivy to something lighter and easier to get in and out of, like a Borah Cuben with side zipper. But for now I am saving up for a new summer bag, so new bivy will have to wait. As for tarp, once I run my Hex solo tarp into the ground, which I hope will be a while, I think I would just replace it with another one, or maybe a Hex solo plus to have more of a palace.
Anyhow been giving a lot of thought to this as of late. I wrote a big long SUL rant on my blog (link in profile) for anyone that is interested, which includes my 2013 SUL gear list. A lot of it had to do with the whole tarp/bivy choice of shelter. I am also a seemingly rare SUL person that uses (gasp!) a ground cover with a bivy, I know. But even with one (and a double one at that) my tarp/bivy combo is still lighter than nearly all tents out there, and could be lighter still with a different bivy.