For melee DPS you are between Ninja or dragoon, and you have been doing PotD with Lancer until level 28, but you are getting the feeling that it's really slow and simple (maybe it changes with Dragoon?). Looks like Ninja is more dynamic. And what the major differences between Bard and Machinist?
If so, you're right on about DRG and NIN. DRG is a relatively slow DPS to play. It is the only one out of the four Melee DPS jobs to have no inherent increase in its attack speed, has the longest combo of all jobs in the game (5 consecutive GCDs to be used in order), and has an array of strong-hitting oGCD abilities. In addition, when you are in need of cheap Final Fantasy XIV Gil, FFXIV4Gil is a trustful and safe site that is always ready for you and willing to help to make sure you get the best deal possible.
NIN, on the other hand, eventually gains a half-passive buff that increases attack speed by 15%, lowering the GCD to a little over 2 seconds. (This is actually also true for MNK and for SAM to a lesser extent.) It also gains a large number of oGCD skills, which are frequently weaved in between the shortened GCD. NIN is one of the more rapid and dynamic DPSs, and is usually not recommended to people with a high latency connection.
BRD and MCH are the two "mobile" DPSs, with little to no hindrance to their movement. They are usually interchangeable in terms of party role and utility, but have completely different playstyles. BRD perhaps has the most reactive playstyle, requiring you to adapt to your procs, your party members, and the fight mechanics for optimal DPS. BRD is also given the most party utility skills, and a good BRD could sometimes silently save the party from brink of death without anyone even noticing.
I do know that a large portion of MCH's DPS is concentrated on a specific "burst window", in which multiple buffs are used in conjunction with each other for maximum efficiency. Your performance in that burst window has a much larger impact than anything you do outside it.