I prefer the disposable foam type brushes, which I clean out and reuse many, many times before throwing away. They're the easiest to use and coat the smoothest (short of using a rod or floating the paper).
However, if you want the brush stroke look, then my advice is to choose your brush based on the properties of the brush. In other words, don't worry about what coats best or looks best, because you're not looking for best. You're looking for character. The problem will be balancing the amount of character you want with the ability to coat evenly enough to serve your photo. And that's going to be on a case by case basis. There's no one size fits all, because it's not just about the brush and paper you use, but also how you handle the brush. Technique plays a huge role. And I'm not just talking about bristle type, but also size and shape of the brush. I'd just buy a bunch of cheap, different types and see what you like best, and then as you figure out what works for you, maybe consider buying some better quality ones similar to the ones you like best. Probably best to stick with brushes made for watercolor though. Brushes made specifically for oil or acrylic only (such as hog hair) may not be able to carry much of that thin emulsion, and be too difficult to use. Or you may like the look enough to be worth it for you to put up with the difficulties of using a coarse bristle brush. Who knows.
As for metal ferrule brushes, there's no reason not to use them. I understand the reasoning behind it, but if you use a brush properly, i.e. don't overload it, then the emulsion should never come in contact with the ferrule. A fully loaded a brush should only be about half full. If you get paint, emulsion, whatever above about half way up the bristles, then you've loaded too much onto your brush and you either need to load less, or get a bigger brush that can hold more. Even when you go to wash the brush out, it should be done carefully and thoroughly enough to not leave any on the ferrule.
One method for balancing evenness with a brushed aesthetic is to coat the paper evenly with a disposable foam brush or a coating rod, and then while the emulsion is still wet, feather along the edges with a brush to get a "best of both worlds" look to it. You might give that a try, especially if you don't have a lot of experience with a bristle brush, as they can be difficult to control. I prefer to use worn out, old bristle brushes for this, as they can often give some excellent effect and character, but be too difficult and unreliable to coat evenly on their own.