londrum - 10:14 am on Oct 31, 2010 (gmt 0)
it depends on which one has got a better chance of bringing in the money.
if you've already got a good conversion rate for people when they visit the site then you'll probably make more money spending it on SEO.
but if your conversion rate is pretty lousy, maybe you'd be better off spending it on functionality, and convert the traffc you've already got.
i dont think people here can give you a definite answer... you need to have a good look at your stats