Most desired DPS job is definitely Bard. With the insane amount of party utility they bring, people would be fools to outright reject a bard and say that they bring nothing to a group. I've heard that Red Mage is actually pretty desired as well, because of their basically instant Raises every other GCD, the ease of the job, and the high mobility for being a caster.

In terms of most complicated to play, that's a subjective measure. However, again, it's been stated many times in the past that Bard is actually difficult when it comes to min-maxing the job. Easy to play poorly, not easy to play well. I would also consider Black Mage particularly difficult in Savage content, because it requires a lot of knowledge with regards to the fight and the mechanics: where they can stand, where they can't, how long they're able to stay still and blow things up, etc.. But, again, subjective measure.