MyISAM is best for heavy writing. By a long ways. For reading, it's much closer to being a toss-up. For mixed usage: Ehhh...I think there is a big fat "it depends..." in there.
But MyISAM does *NOT* enforce referential integrity (that is, even if you use Foreign Key constraints, they are ignored). For 90% of normal DB usage, you are better off with INNODB. But only if you then also actually code and use foreign keys.
Unless you are trying to add gigabytes of data per hour, I'd stick with INNODB.
An optimist sees the glass as half full.
A pessimist sees the glass as half empty.
A realist drinks it no matter how much there is.