Im killer with combo's on round 3.. Never played online so i dont really know how good i am...
Have had some absolute wars with friends though..

I always use the fast hands with slickster style cos i box and counter...

things like jabbing away..Moving to the left throwing two or three jabs..
then a one two left hook to the head lean back make em miss hit em with a counter right and a left hook..
I love to put punches together on fight night.. It helps when you have the fast punch style though cos you can lunge in with hooks and follow as they retreat after a few punches...
Also its always great to mix up your punches and go to the body.. And maybe even go back to the body after going to the head.. Get plenty of combo's that way..
Peace