I hope by giving you an idea of what each class is might help you decide:
Melee DPS:
There are 4 of them. They rely on staying up close and landing some positional attacks. Their Limit Break is all about heavy burst to single target.
Dragoon(DRG): DRG is all about 2 long combo strings (5 hits) and oGCD "Jump" attacks. It has a highly coveted raid-wide crit buff, a targeted damage boost to friends, almost doesn't exist on aggro tables because of its ability to dump it by half, and most importantly, the bard's best friend, a huge advantage considering bard is the most sought after job and most good bards refuse to not have a DRG in party due to high dependency for optimal damage. Dragoon is sadly on the low side of personal DPS (bottom 2).
Ninja(NIN): Ninja is probably the most "true" to its class fantasy in the FF franchise. It has a very interesting (or cumbersome if you're not into it) spell system in the form of Mudras to form ninjutsu. Naruto fan's best friend (and I hate Naruto). Has a "misdirect" ability along with Smoke Bomb (reduces enmity of a friendly), has trick attack. Oh and it brings slashing which tanks really want, but it's one of 3 that can. NIN is in the bottom 2 in terms of personal DPS... Competing with DRG. Outside of what I find stupid up-time mechanic in Ninki, NIN has a very fun rotation where you juggle and keep track of your GCDs, off GCD attacks and Ninjutsu.
Monk(MNK): In the top 4 DPS (going between 3rd and 4th based on fight and patch). Heavily dependent on positionals. MNK is about positionals and Greased Lightning and later on it is about how fast you can rebuild GL back. Has ok utility (Mantra is very good for progression). A good monk needs to pay attention to their enmity as their way of dropping it outside of the initial suppression from Diversion costs them DPS.
Samurai(SAM): Top 3 DPS (going between 3rd and 2nd, been 2nd all of this tier) and SE seems to want them to be always in the top 2. Least dependent on positionals. Absolutely selfish class. Least affected by using Limit Break but no Samurai in PF would use it sadly. They also bring slashing resist down, but again, one of 3 jobs that can.
Caster DPS:
They, well, cast! Out of the DPS jobs they have the best AoE, useful in dungeons but almost irrelevant in raids. They have comparatively limited mobility. Their limit break is big AoE of big damage (half what melee does).
Black Mage(BLM): The. Top. DPS. BLM is about landing as many <insert biggest explosion here> per cycle in its rotation, which in order to achieve so you have to juggle buff timers. Simple at its core, a bit harder in practice. It has good bursts of movement, but with a cooldown so you have to plan ahead (which is where its "difficulty" comes from). A good black mage will beat a similarly skilled SAM by a mile. But if you thought SAM was selfish, BLM makes it feel generous. There are 2 ways for this job to destroy the meters, being an absolute beast skill wise, or being catered to. Top parses usually involve both. This class is an absolute turret that does its best when stationary. It has good bursts of movement, but with a cooldown so you have to plan ahead (which is where its "difficulty" comes from).
Summoner(SMN): The best caster and, in my opinion of course, one of the best jobs out there with bard, scholar and paladin. Top 4 DPS (currently 3rd/4th in a competition with monks). Brings very good utility in the form of magic vulnerability debuff to increase raid magical damage or a reflect shield that reduces target's physical defense and doesn't reflect anymore.. And a battle raise (not as spammable as RDM) and has very good MP management. However this job comes with a high learning curve (once you learn it you pretty much cruise control it). As far as mobility is concerned.... It's not a concern for SMN due to the myriad of instant spells (comes with potency loss however). This job is good for progression AND farm/optimized runs. Oh it comes with the bonus of Scholar being leveled as well (arguably the strongest healer).
Red Mage(RDM): With the recent buffs, RDM is in the higher half of the DPS classes damage wise. It has decent mobility (based on how you define mobility mind you). Due to its intended innate DPS mechanic for its rotation, this class is capable of instant casting raises and can bring back multiple party members to life saving wipes. Making it a very good progression class. It has Embolden which is a physical party's, erm.... very good friend? lol
Physical Ranged DPS:
Nothing restricts these guys outside of range. Very mobile and as such are usually your go-to when you want a mechanic handled. They also fill a very good niche of high support. They are so useful that some argue that they do too much damage for what utility they bring. Their limit break is a line AoE.
Bard(BRD): The mandatory job. It is in the lower half the DPS numbers, but it's understandable considering it has the highest raid DPS contribution. Packed with abilities to restore everyone's mana and a myriad of defensive and offensive buffs, brad is "The" utility job you want in every group. For this job to perform well however, you NEED a DRG (giving you between 15~20% of your DPS) due to heavy reliance of a vulnerability debuff that you can't apply yourself, and you want a SCH.
Machinist(MCH): A decent bard replacement..... That is a lot harder to play (due to clunk and pink reliance). Has the same mana refreshing abilities but less quantity of defensive and offensive abilities, albeit more potent due to frequent use (shorter CD) or steady nature (i.e. damage% instead of crit chance). DPS-wise it falls right in the middle. Takes a lot of skill to play effectively due to aforementioned ping reliance and slightly complex rotation.
Please note that the gap between the highest DPS and lowest DPS in terms of personal DPS does NOT matter because of utility and/or other balancing factors that makes up for the gap. All DPS classes played well will meet DPS checks and do more than tanks in terms of DPS so do not worry about your job being in the lower half or even "bottom" DPS. NIN and DRG, while the lowest 2 DPS jobs, are almost a stable (some groups will ensure they have them more than tanks). Also in case you haven't noticed, there is some bias in my post. lol
I hope it helps you decide. If you want to try tanks or healers, I recommend: WAR > PLD > DRK for tanks and SCH > AST > WHM for healers. (I enjoy DRK and SCH most though).