My first two tarps were a Warbonnet Big MambaJamba, right when the Blackbird was first released, and a Speer 8x10.
The two were like night and day. The BMJ was easier to get a tight pitch with, provided better coverage, and really didn't add much weight or bulk.
From there, I upgraded to an absurdly beefy OES 12x10 that I deigned to mimic the 11x10 Speer Winter tarp, with extra tieouts in the middle of the cat cuts for "emergency" situations where more flexibility in pitching options would be useful, and I've used those extra tieouts extensively. Not long after that, MrsMustardman sewed her Asymmetrical Winter Tarp, which I was hoping would become a more popular design, but never really took off. Still, for a hammock with a clearly preferred entry direction, like the Blackbird, I think this tarp is one of the best we own for maximal winter coverage and weather resistance. You can pitch the narrower side into the wind to help reduce the sail effect, and still have plenty of room on the other side of the hammock, especially if you use a grip clip or panel pull to make some more space on that side.
I've settled on the 12x10 size as my preferred tarp size - the 10 foot direction is good if you need to rotate the tarp if your trees are close together or whatever, and the 12 foot gives you the extra ridgeline coverage to keep your stuff dry even in "porch mode" with moderate wind. It's also a size that works quite well for two hammocks under one tarp, which is my preferred way to hang.
That said, I might have something even more ridiculous coming soon, car-camping only, but it will be a lot of fun....