Wow, tough question... It's like asking would you rather be blind or deaf? Neither!

If it were one or the other, I'd take cognitive function. Like VenusHalley, I really value my intellectual performance and if that's compromised it has a strong negative effect on mood. Whereas stable mood but bad cognitive function would actually be something I can't imagine happening - when my brain doesn't work, it makes me very, very distressed.

I don't know if I'm getting memory side effects from Lamictal because I've always been a bit scatterbrained (ADD, actually). The word-finding thing, which I have problems with when depressed, has been more prominent lately. Mildly irksome but not all that bad - just annoying because the words are on the tip of my brain but it takes a long time to pull them out. I'm guessing it's noticeable right now just because I'm doing a lot of writing but otherwise it probably wouldn't be something I'd pick up on.