Truth to tell, I've never really given it much thought. I like hickory or shiro kashi for bokken as they tend to last the longest, and a good sized tsuba to protect my hands from over-zealous partners is nice, but that's about as far as I've gone when thinking about bokken. In the arts that I've practiced, they are considered consumables and will get beaten up from contact. Therefore, not a whole lot of thought has ever been aimed at things such as balance or weight.
For beginning HNIR students, the bokuto used are generally rather light. As they progress they can use heavier ones.
Since my other arts (German longsword, etc) use steel nearly exclusively, most bokuto feel on the light side to me.
Many HES practicioners are rather particular about their wasters though. New Stirling Arms makes some of the finest wasters on the market. Might want to take a look-see at them to find out what people have asked for in the past. Kim Taylor makes excellent bokuto for JSA, BTW.
I've been using one of Kim's handmade hickory bokken, http://sdksupplies.netfirms.com/ with a moosehide tsuba for almost 11 years now. I've used it all that time for iaido and for jodo and its as good as new IMO.
I like something that approximates the weight of my shinken, something too light or too heavy just doesn't feel right in my hands. Though I do keep a "heavy" jo on hand for special occassions.