At the end of the day, for your purposes (running off a 2S lipo) there is very little difference between the two. A switching regulator "should" run a bit cooler than a linear regulator and for a well designed switching reg the ripple is a non-issue.

So it comes down to comparing size, weight and amp rating.

I've always run the Castle 10A switching BEC in my small electric stuff and can't say a bad word about them, but I run linear regs (homebuilt) in my IC F3A ship, 10A for the plane and 5A for the cdi running off the one battery. I also tend to think that if something does go pear shaped with the regulator voltage source (??) that a linear reg is a little more electrically robust but I've got nothing to back that feeling up with.

Oh, a linear reg set to 6V will need a minimum 6.5V input (0.5V overhead) to be able to regulate, I've never tried to figure out the overhead the Castle switching BEC needs?