spamassassin database

[John G. Heim]

Right now I have the spamassassin bayesian rules database in mysql myisam 
tables on our mail server. I want to move it to our database server. 
Mysqltuner tells me that the read/write ratio is 10/90. 90% writes.

Given a database that is doing 90% writes, what database engine should I 
use?