I only currently sell on Amazon and eBay, so not sure if this is relevant to Etsy, but I would probably go with ‘free over $35’.
I’ve only encountered 2 customers on Amazon who’ve told me - I only buy things with free shipping. My casual, completely unofficial observations, say it doesn’t matter to most people all that much, unless, possibly, you have a lot of competition and you’re trying to gain an edge.
My impression is that full free doesn’t really make any difference at all with sales volume.
I would agree. What matters more is if people want what you’re selling. I have a small item on which I charge shipping. I’ve had many customers who place two orders back-to-back, either to buy more or add a variation they forgot, it’s unclear.
But when they do this, they pay shipping twice, once on each order, and they never seem to notice. It happens often enough that I wonder if they don’t notice there’s a shipping fee, or just don’t care? This happens primarily on Amazon.
I have a couple ‘free shipping over $xx’ promotions on eBay and they only attract occasional interest. Most of the time, it seems, people just buy what they want, and pay whatever the price is. eBay shoppers often seem to miss the (big, obvious, IMO) red text on the page that says - PROMOTION!! Spend $xx and get free shipping. 
Sometimes, I get messages asking if I combine shipping, and I’m like yes, but - did you notice that it’s free if you spend $x? Of course, they never noticed. People are strange.
If free vs paid doesn’t impact your sales volume, then free over $xx might benefit you most, as it might encourage a few people to spend a little bit more to get the free shipping.
But I’m free on Amazon so that’s always a concern - that someone will find it there and be angry.
Do you get many customers that shop for the same product on both sites? Even if they do, it seems unlikely they’d notice. Everyone seems in such a rush these days, and rarely slows down long enough to pay close attention to anything.