I have been curious as to which method of CSS styling is quicker (rendering wise) and then from simply a best practices perspective which method makes more sense (pretty subjective I would say?).

I can create base classes like:

.rounded-corners-5 { -moz-border-radius: 5px; -webkit-border-radius: 5px; border-radius: 5px; }

OR

I can do the other method of applying styles to multiple IDs/Classes:

#box1, #header, #container, .titles { -moz-border-radius: 5px; -webkit-border-radius: 5px; border-radius: 5px; }