In my opinion, trading and bounty is not something you consider "either or". They are both independent of each other and since it does not belong to "either or", why not both together?
Signature campaigns do not require much time, furthermore you can only join one at a time, until the campaign ends. As long as you are active in bitcointalk, signature campaign may only take up an insignificant portion of your day and you can leave the rest to trade.