Everything always prefers tertiary, BUT this is a complicated question.
I pulled out the big Princeton book.
Here are the numbers: TERTIARY SECONDARY PRIMARY
BROMINATION 1640 82 1
CHLORINATION 5.3 3.9 1
But it also depends on how many hydrogens are available.
If there was 1 tertiary and 1 secondary hydrogen then the the Chlorine will bond to the tertiary one because as you can see it is more favorable (5.3>3.9). But if there were two secondaries hydrogens and 1 tertiary then it would add secondary (2 x 3.9>5.3)
For bromines, ALWAYS TERTIARY, unless you have a 20 to 1 ratio of tertiaries to secondaries.
Chlorine is more desperate to add than Bromine. Chlorine reacts faster.
Hope this helps, took a while to write....
Stability favors the radical on the tertiary carbon however chlorine is more reactive due to its higher electronegativity and electron affinity thus it discriminates less.