There is no cons in dual boot until a clear boot loader is configured to boot both the OSs.
If you have more amount of RAM, and have any purpose to use both the OS at the same time, virtual machines are good.
And Ubuntu makes your life easier. Will let you to use your internet, without any extra work, which can be used to solve any upcoming problem if any.
If you dont have more amount of RAM then Vitual box may not be a good choice, since Running 2 OSs at same time need some more main memory[RAM] . Dual boot option wins here.
And if you dont have any purpose to use both OS at same time, by dedicating some 1-1.5 min[ shutdown current OS , reboot, then get into another OS] in dual boot, will reduce the system load in a notable manner .
In Windows-7 , I have a good experience with Ubuntu as Guest OS.