If you "have to" do tons of cardio to stay lean, your diet sucks. Here's a little realty check.
You need some type of cardio, but probably not as much as you think. If you do need a lot, then your diet sucks, dummy.
Cardio, whether steady state or interval style, is important in body recomposition. Doing it in moderation in comparison to your weight training is far better than getting crazy with cardio in order to recomp.
Function Creates Form
Remember that your function will create your form. The more steady-state cardio you do, the more your body will adapt to meet those demands. So over time, you're probably going to look like someone who, well, does a lot of steady-state cardio.
Interval training tends to be more anaerobic and can be done in short spurts that boost basal metabolic rate for a good deal of time after the session is over, unlike steady-state cardio. (For workout ideas, check THIS out.)
There are benefits and drawbacks to both. But unless your goal is to look like a jogger, keep the steady state work to a few times a week for 30 minutes a shot. Make sure you're working hardest on your diet in order to get leaner. A few weeks of steady state multiple times a week can get you out of a rut. But more times than not, you probably need to assess your diet instead.
Remember, if you "have to" do a lot of cardio to stay lean, then your diet stinks. Period.