The frame is the most crucial part of a build. It dictates the handling characteristics and also what's capable of fitting onto the drone. There's no size that's better than the rest, each has their own pros and cons and most people have an array of sizes in their arsenal. The bigger the frame, the more components and more importantly, the more battery capacity that can be squeezed onboard. Most long range builds start at around 7". However, most drones built for racing and agility tend to use smaller frames such as 5" and below.