Beastman mobs, or anything 50 ish give the fastest bonding. It'll go faster if you have HQ gear by 20% I think? and then another 20% if you meld materia into it (yay shitty cheap lvl 1 materia) and also 20% from FC buff I believe? Makes for 20 minute bonding or less really. Grab the potion from your GC for +3 spiritbond and wear the gamblers crown for another +1 (dunno how much difference that makes really).
Most of us bond with crafting gear but the market for that has been super shit lately, gathering materia (leather sets) sells higher but takes a little longer to sell. Things like tourmaline and all those sets convert into materia needed for relics but also some useless materia (yay elemental) so you have to hope for the best rng luck.
Spiritbonding item lvl45+ can convert into lvl 3 and 4 materia which sell the best but you have to kill mobs +-6 levels of the gear you are bonding for the best speed.
Mostly hope the rng gods favour you, pick whatever is cheap to buy or make or whats selling well materia wise and lose your mind grinding mobs eternally (and level your choco buddy because he needs love too)!