I can't say what job is least-played on my server/data center (while I want to say SMN/MNK...that's ALL I run into when I DF as a tank >.>) the jobs that seem to be in highest demand for statics are SMN and melee (with a shift towards DRG; occasional need for tanks and heals, but I've seen a ton more PFs LF SMN and/or melee). Now, this doesn't mean that these are the least-played jobs, but that they are the least-played well.

I do see a ton of BLM and BRD still, with slots for those filling fast in PFs. There are still a large number of DRG in PFs...but the majority are just bad (which is why groups always seem to have open DRG spots...). Depending on content, healers or tanks are usually last to fill (Ifrit, T1 and T4, Tanks are rare. T2, T5 or Levi, Healers are never around)

And I do see bad examples of every class, a lot. Its most obvious when a Heal or Tank is bad but bad DPS also drag parties down (I hate seeing BRD die to easily avoidable AoEs...the one class that has almost 100% uptime while dodging...and yes, I've had some say they couldn't dodge because they were DPSing and moving is bad...really? You are not a BLM!)

Pretty much, if you want to "be wanted", roll a tank or heal...but make sure to be a *good* tank or heal. If you want to DPS, don't roll a BRD or BLM, and if you roll a SMN or DRG, make sure you are really good at your job (MNK, well yeah, be good at it, but from what I've seen from MNKs outside my static, its easier to pass under the radar since their DPS is naturally high as long as they keep up GL3 and positionals are more forgiving to them than they are to DRG)