Depends on what you want in terms of sound quality.
For most gamers and desktop users, the sound quality from headsets is sufficient. For serious audio people, the sound you get from gaming headsets they would consider low quality so they will use their premium headphones paired with a microphone. Having a mic on the headphones is definitely very convenient. I use both actually as I can't stand using a standalone mic: Sennheiser PC360 for gaming and AudioQuest Nighthawk for everything else.
Get a headset if you aren't looking for premium audio quality. Premium being headphones that cost over 500USD.