Equity Home Mortgage

If you make extra payments, it is better to pay on a mortgage or a home equity loan?
I'm guessing this will vary based on loan detail, but generally if you make extra payments, it is better to target mortgage (30 YR. solid, 80% of the purchase price) or a home equity loan (15yr interest only around 20% of the purchase price) just to ensure that the issue is clear … which is better to do (as far as making better economic sense)? Apply extra on a mortgage or apply for additional home equity loan? If I can only use the extra payment against one or the other.
I think that if you go 30 YR. fixed with 20% down you get into a more stable program (in case something comes up where you can not make these high payments) and then when you have extra money you make one extra payment, but be sure to tell them to "Use IT to the principle of" the way it goes against the original loan amount Instead of going in the direction of interest. This way you can pay your loan earlier and save yourself thousands in interest. But I'm definitely not an expert, just some others who will through all this BS loans