bootcamp is dual boot where the operating system run directly on the hardware
parallel is a virtual machine where an emulator is running on top of OS X
reliable depends really when an operating system run directly on top of the hardware 3d video card features can be used
but when it's real drivers rather then emulated generic drivers a bug in the driver can cause more risk of crash then the virtual machine where the video cards features are not sure
same with other stuff driverwise
but with a virtual machine the memory and io transfers are shared between the virtual operating system and the real one
and as stated the video cards 3d feature will not work so 3d games or 3d modelling software is run poorly of at all