The issue with a virtual machine is that it is running your native OS and another "virtual" OS; as you can imagine, this can be slow. Booting up your virtual OS also takes longer seeing as you functionally need to boot two OSs rather than one.
In terms of dual booting (installing an OS alongside your native OS -- in this case Windows), the resultant OS typically will run faster and won't be bogged down as much. If you have a lot of RAM you might not notice the speed loss though. That being said, it is much easier to install multiple virtual machines than it is to install multiple OSs; your hard drive won't be chaotically partitioned since virtual machines don't need separate partitions.