Based upon everything I've read and heard from some pretty sharp people... it depends. Examples:

Annular boosters promote better atomizing of the air-fuel mixture, but they can work "too well" and result in less power, although improved efficiency. They're also more sensitive to temperature changes in the induction system. In certain applications they're more difficult to tune, such as large c.i. engines trying to run a 4150 annular and going rich early because the annular boosters come onto the main circuit faster.

Downlegs can be problematic when there isn't sufficient signal being made to pull the fuel through the booster and break up against the inside of the booster venturi. You can find some good videos of carburetor operation viewed from above the venturi and under these low-signal conditions the fuel comes out more like it's pouring from the end of a (very small) garden hose, barely touching the booster venturi.

Well, that's what (some of) "the experts" say. And then you look around at moden 4500-type carbs and rarely see anything but annular boosters... and the current lineup of Braswell 4150-type carbs doesn't appear to use anything but Braswell's design of downleg.

I cannot claim anything conclusive. Even if my future planned carb tests show an advantage of one approach over the other, that would only be valid for my specific combination & application.

Yep, that's a really long non-answer, but it's all I can offer at this point. Not having real test results sucks.