Though many popular recording programs such as Pro Tools, Ableton, Cubase and Nuendo run on both platforms, some are unique to one system. As of 2010, PC systems exclusively run Sonar, Fruity Loops, Sound Forge and Adobe Audition while Mac systems exclusively run Peak, Logic, Garageband and Digital Performer. Your client base and software of choice is an instrumental factor in the decision.
Mac computers are typically priced above PC computers with similar system specifications. PC's parts may be repaired or upgraded often more widely and for a lower price while a Mac is more expensive, and it is harder to find someone to repair or upgrade the computer.
Most plug-in manufacturers release their processors in a variety of formats covering most operating systems and software. However, in some cases certain plug-ins may only run in a specific program or on a specific platform. In general, there are more plug-in choices and virtual instruments available for the PC.
Sound quality and processing power of both systems are comparable. The ultimate decision comes down to budget, compatibility with clients and other studios, software choice and personal preference.