In particular, how do you choose between MyISAM and InnoDB, when neither is missing a required feature (e.g. you don't need foreign keys).
Does it always come down to trying both and measuring? Or are there good rules of thumb regarding the number and frequency of reads versus writes, and other measures like that? Does the size of the table have any effect on the typical choice?
(Although I've tagged this as subjective, since it seems like it is, I'd prefer as objective answers as possible).