OK, as far as I know, the body is not capable of being in a muscle building phase while also burning fat....unless you are completely new to lifting and exercise, in which case you can get away with some muscle gains and fat loss.
With that said, if you are serious about getting into shape, concentrate on getting a solid lifting routine. Also keep your diet in good condition, that has everything to do with your sucess. So, to answer your question, HIIT is better to do than longer, moderate cardio if you are a lifter. It gives you excellent benefits, while not causing your body to consume muscle, which can happen with longer cardio sessions.
Me personally, I'm concentrating on lifting. So, I am not the most disciplined about the cardio aspect, but I try to do 2 HIIT sessions a week (that's all you should ever do) and 1 longer cardio.