Another vote for the 39.5. I went through the same process with another watch (Oris Aquis). I owned the 43 for years and loved it, but found it a little too big. I tried on the 39.5 several times and found it a little too small. I eventually gave up, sold my 43, and have been wearing/loving a 36mm Tudor for the last year... go figure.
Without wearing each for a while, it's hard to decide which is best for you. I realize now that if I'm on the fence, I'm probably better off with the smaller watch. They may look out of place in the AD next to their bigger brother, but living with them day-to-day, they feel more natural on my wrist and fit my personality/style better.
Both are beautiful watches. You might just have to take a leap on one of them and spend some time with it. Or you could check out the newest Aquis, which is coming out in 41mm 😀