GarageBand is great for recording vocals and you can achieve a very professional-sounding performance. However, other DAWs provide more control and options over vocal editing and effects, giving a more professional sound than Garageband. This doesn't mean you can't achieve a professional sound in Garageband! It mainly comes down to the quality of the singing itself – if your vocals sound bad then there’s not much you can do to fix it regardless of how good your set-up is. However, it is a good idea to invest in a good microphone to cleanly capture vocals and improve your music production setup. Many artists and people in music production have used GarageBand to create professional-sounding vocals and the effects it offers are more than capable of achieving it. Using a plug in like Antares Auto Tune in a GarageBand project can make your vocals sound amazing.