They are both pretty hard! Front aerials are difficult to do because they require both a lot of flexibility and a lot of strength. many tumblers, acrobats and gymnasts tend to excel in one area over the other. ie lots of strength but not much felxibility or vice versa. But to do a front aerial you must excell in both area's.
The flexibility required is that of your back. Most people can do good front walkovers due to their shoulder flexibility but that will not help with this skill. You need a very flexible back, which is a difficult type of flexibility to gain if you are not naturally born with it.
Anyway to do a front aerial it is important not to think of it too much as a front walkover. A front walkover is a controlled skill close to the ground. A front aerail requires a strong push uff the ground. In must go up.
A good way to develop the skill is to practise dive front walkovers. This helps you practise pushing strongly off the front leg. Practising them on the trampoline or tumble trak is useful too as it helps you to break the habit of putting your hands on the ground. The biggest problem people tend to have learning any type of aerial is breaking the habit of putting hands on the ground. As you can do a side aerial you will understand. It feels very different to do a side aerial on the floor to the way it feels to do it on the tramp, but doing it on the tramp makes it easier to train yourself to keep those hands up.
When you are doing the skill aim to get your first foot onto the ground right underneath your nose.
I would tell your coach that you are interested in learning the skill as it is a difficult one to learn with out an experienced spot. It also can be quite a dangerous one of not learned properly and safely.
for a side aerial:
You need to lift as high as you can. You need to feel like you are pushing up with your bottom leg. Start with a run and a hurdle for more power. If you keep putting your hands down try hooking your thumbs under your bra straps. Only do this if you know you will not fall on your face. Also try doing an aerial up onto a higher surface (a soft higher surface). After you have done several onto a higher surface (you probably won't land it) try on a flat surface again. Use the same action that you did for the higher surface and you should land it. Don't not try less than you did on the higher surface just because you are not going on to a higher surface. If you try as much as you did on the higher surface you should get enough height to land it on a flat surface. I used to put my hand down because I was scared but I knew I could make it to my feet so I tried it onto a soft mat with a small run up and hurdle. I put my arms out straight while I was upside down and I did not feel the need to put my hands down. Good luck and do not hurt yourself