You can mine to either port, but mining to 13333 is mining the test code with segwit activation flagged, and while the code has now been bugtested and appears to be working fine, I give no guarantees with it (though I'm almost certain it should be fine now.) If the lack of guarantee concerns you, or you wish to not signal support for segwit, mine on the regular port 3333, though once the test pool finds a block successfully, I will not be giving an option against segwit.
Well, clear and lightning quick answer. Thanks, -ck! As I treat my solo minig once a week as a lottery, I do understand low chances of winning, so the lack of guarantee is smth that scares me least of all)))
So i'll go to 13333, hope to become the one who proves with a block the test code works fine