The best boards in my opinion are the mining sections. Great insight, no spammers, no trolls, barely any paid sigs in the mining boards.
Mining sections have less spam than general discussion but you will still get megathreads and vague, pointless discussion.
The fact of the matter is, unless the section requires a degree of sophisticated knowledge, you will get posters who will spam the same redundant common-sense crap everywhere.
Something something bitcoin trends go up.
Something something house edge.
Something something merit is good.
Technical Discussion might be the most spam-free part of the forum because (let's face it) most people here
still don't know how Bitcoin works. On the flip-side, you have the spam-ridden "good project sir" Altcoin Discussion sections, which should be set ablaze.
(Technical
Support is half-half. You'll only get good discussion when the thread is not about "my transaction isn't coming through!")