I think the main thing is just to do what you ENJOY and can STICK to when it comes to cardio. There is alot of information saying HIIT may maximize your time better than light cardio, but alot of people have a hard time sticking to it for longer periods (me included). Target heart range can also play an important factor in maximizing your cardio for fat loss so it may be worth your time to read up on that.

As long as your diet is in check and your not going crazy on the cardio, you shouldn't have much to worry about when it comes to muscle loss. Sipping on BCAA's etc through the cardio can also help prevent muscle catabolism if your really worried about it. In the end its all about calories in verses calories out.