Zipped! I left my new to me Epi Speedy unzipped the other day when I got out of the car and somehow managed to spill the small quantity of water that was left in my travel mug on my bag. Of course it went right inside because the zipper was open. :/ Luckily no damage to anything, but I won't leave it unzipped again.
I'm not giving potential thieves a peep show. This reminds me of a viral store video showing a pair of thieves stealing a shopper's wallet out of her LV bag without her ever suspecting it.
Always open (either a 25 or 30). I feel like they are pretty secure due to the short handles. Might be different with a bandouliere although I think I'd still keep it open as I tend to put my hand on my bag when it's cross body.