IMHO, if you don't just fall in love with one particular job and want to level that one up to 75 first, instead simply level a ton of jobs to 40. Then pick one you like best. Soooo many jobs are also great sub-jobs that you almost need them all to 40 anyway -- especially once you reach 75 and start needing to specialize your main job for different HNM fights. Also, the gear costs for 0-40 are so low that you actually will earn gil leveling all those low jobs. When it comes time to push to 75, you'll be able to afford it without any gil-farming pauses even if it's one of the "costly" jobs like RNG or NIN.
Pretty much every job will find a use for these jobs as sub-jobs at some point: blm, whm, rdm, war, nin, drk, thf, sam, dnc, ... hell, just use the whole list. There have been a ton of times when I wish I had all jobs to 40 just so I could sub the most appropriate job for the occasion. Going back to level 'em all up will probably be my next "xp'ing goal" for this game.
BTW, why 40 instead of just 37? Many of those jobs are useful in level-capped BC fights. Level 40 is one of the potential caps. You'll be able to fit into a wider selection of 40-cap fights if you have more level-40 jobs. This is nice for both PMs and other BCs.
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