A round paint brush is the most traditional brush shape, and what most people imagine when they think "art paint brush". A decent round brush will come to a lovely sharp point, enabling you to paint fine lines and detail with it. (This is especially true if it's a brush made with top-quality Kolinsky sable
hair.) Look for one that's got a good spring in the bristles, where they snap straight when you take the pressure off the brush.
The round brush in the photo has synthetic hair in it, and didn't have a very fine point even when it was brand new. But I bought it as it would be useful for creating broad brushstrokes as it's very soft and holds a good quantity of fluid paint. Always consider what you intend to do with the brush; don't have unrealistic expectations of it or you'll just frustrate yourself (and blame your tools for poor painting).