MyISAM and MySQL
MyISAM Storage Engine is the type most commonly used. This Storage Engine allows indexing the whole column (Full text index) so that it read access speed for the fastest performance.
However it is very poor in the "insert / update" data. So if your website is mainly cms as wordpress blog, you should choose this type of Storage Engine.
InnoDB in MySQL
InnoDB Storage Engine is newer MyISAM, this Storage Engine is the best for Forums have constantly updated amount.
Speed ​​insert/update/delete operations preferably by Row Level Locking mechanism so when updating (Add, delete, edit) 1 table, only the records are being locked alone operations, other operations on this table still occur normally. But its drawback is cost more RAM to operate than MyISAM.
MySQL MEMORY
Engine MEMORY (HEAP) engine speed is retrieved and updated best because it stores data directly to RAM. Therefore it is used as the data table contains three or user session. When restart MySQL or Server, all data will be erased.