Talk to plenty of guitarists who think they know a thing or two about the instrument and you'll come away with the implied truism that a bolt-on neck is inferior to one that is permanently glued in place. Such "accepted wisdom," however, simply isn't correct. The two types of neck construction contribute to guitars that are different, sure, but this isn't a "better or worse" relationship. Part of the misconception comes, no doubt, from the two major brands that display these different types of neck construction: Gibson and Fender. When compared to Fender's basic, slab-bodied guitars with simple finishes, no binding, and necks attached with wood screws, Gibson's higher-end models like the Les Paul often look fairly elaborate, formal, and traditional. Not only do they have glued-in necks (also known as set necks), but they have binding around the body and fingerboard, carved tops, multi-wood body construction, more deluxe inlays, and other elaborate features. In the face of all that, though, the different ways in which these guitar's necks are attached play little part in any qualitative assessment of the instruments as a whole.
Today, high-end guitar makers build extremely good — and very expensive — guitars made with both types of necks. If they are building a "Fender-style" guitar, they'll usually use a bolt-on neck; for a "Gibson-style" guitar, a glued-in neck is the standard. Plenty of others also make entirely original designs using their neck format of choice, according to what they hope to achieve sonically from the instruments. Aside from the mere fact of how they are made, glued-in and bolt-on necks enhance slightly different sounds in the guitars on which they appear. A glued-in neck transfers the resonance between neck and body more freely and immediately than does a screwed-on neck, which enhances the warm, round, thick tone that many such guitars are already predisposed towards (think Gibson Les Paul or ES-335). A bolt-on neck, by comparison, generally contributes to sounds in the attack and tone that are referred to as "pop," "snap," or "twang" — characteristics that are already part of the classic bolt-neck tonal palette (think Fender Stratocaster or Telecaster). On top of any sonic contributions, the bolt-on neck is often easier and less costly to adjust, repair, or replace, and it can be less prone to damage if a guitar is dropped. Otherwise, there's no better or best to debate. The two approaches are just different.