freebase is an oil. Its sort of ok to burn but its very strong. Remember that tiny bit of FB oil turns to quite a lot of HCl salt. So one spot FB oil = lots and lots of spots of the salt. So watch out or you will blow ya socks off... FB oil not at all convienent to handle, which is why it is turned to the salt. So you might as well just do that anyway. It doesn't make any difference to the metabolism in the end. Just easier to use. And may be more prone to pyrolysis in FB form too like Chemo said.
MDA/MDMA is an oil too in FB form. In fact most PEA's probably are. Other beez will know more about that, not too sure about that really. PsuedoE is a solid in FB form thou. Well, waxy soft shit, not really 'solid' as such but not an oil anyway.