I've used Parallels and Bootcamp. It depends on the software you want to install.
Bootcamp will run Windows natively. In other words, just like any other Windows computer.
It will download drivers for the onboard video processor. The Mac OS is not running, so all resources like RAM are available for Windows. Bootcamp is free, but you have to own a Windows license.
Bootcamp will partition your internal SSD. However, I believe you can install Windows on an external drive.
Make sure your SSD has enough room for the Bootcamp Partition.
With Bootcamp you cannot switch between Windows and the Mac OS without rebooting.
The same it true with Parallels, you have to own a Windows license. You must also purchase Parallels.
Parallels is an application that runs on the Mac OS. You can easily switch between Windows and Mac without a reboot.
While running Windows, the onboard video processor is not used. Parallels creates a virtual video processor. If your software is video intensive, you're better off with Bootcamp.
Parallels and Windows also share RAM. You can adjust the amount of Ram dedicated to each OS or have it choose automatically.
Software like Quickbooks will run very well. Software like video editing will not run well at all.
