In my eyes, twisted wire makes the design look much better - beautiful & professional.
You can buy an already twisted wire at various suppliers on the web (I personally know that Fire Mountain Gem has it in sterling silver and filled gold...
Or
You can twist your own wire using spin vise or an automatic screwdriver/driller. In these cases you'll need to use a dead soft wire and be careful not to twist it too much so it won't break!
You can find free and paid tutorials that uses twisted wire in their designs by searching the web.