Kinda what Werhusky said...

Well, nobody knows how things will change for the expansion, but right now, the 2 jobs you were looking into (BLM and SMN), might not entirely suit your needs...

You want big numbers, I don't know if you mean high DPS or actual high numbers popping up, but BLM has the big numbers coming up, while doing middle of the pack DPS. Although, they are not the most hard job to play... It's not as easy as some people make it out to be, but you will get a hang of the rotation in no time at all, and once you have practiced the movement (you want to stay still as much as possible, cause you can't cast most of your spells while moving), it really isn't too hard.

SMN on the other hand, are a lot more challenging than BLM, and people would acknowledge you if playing it good, but they also don't have much big numbers... It's a DoT based job, with Fester being their only big numbers spell at all pretty much. Their DPS is too low at the moment too, but I doubt that's going to be the same in the expansion.

If you really want those big numbers, and have some challenge doing it, NIN or DRG is for you... They both have high DPS, high numbers and they are tricky to get the most DPS out of them. Some people might argue that NIN and DRG isn't so hard, but I very rarely see any melee DPS at all actually, that gets up to the numbers you would expect from them. After all, how hard a job is to play, should be "measured" when you get those bigger numbers, not just get through your rotation decently.

Look out for NIN though, if you have higher ping, or ping spikes, I don't recommend NIN actually... it's too hard using their mudras effectively.

Although MNKs doesn't get as big numbers, they are at the top when it comes to DPS (maybe sharing with NIN), and they are very challenging for a lot of fights. Easy rotation, but hard to apply in many fights.