After shooting many years with my S&W revolvers I say it is a large advantage to chamfer the cylinders. Stay away from the star unless you like cartridges falling under it during a reload.
Just breaking the edge of the cylinder is preferred if you want a carry gun but if you want to break the 2 second reload with speed loaders during competitions go as much as you can without taking too much off to un-support the case and cause a rupture.
There are proper tools to buy that will help but you can also get buy with a (God Forbid I Say It) Dremel. Use lots of oil and go slow. Remember too much looks cool but will eventually hurt you for reliability.
For speed reloads I recommend Safariland Comp III or Jet Loaders. It helps to tune them as well but that's a different story.