When deciding on Procurement Orders to send Auxiliary on, should I focus on level req or EXP reward?

I ask mainly because the level requirements for Floating Facility, Daybreak Province, and Nightfall Province are lower for the required items, but reward more XP to the player once turned in.

Does this also translate into FF, DP, and NP procurement orders giving more XP to auxiliaries? Or should I stick to higher-level ones like Dragon Altar and such for leveling my Auxiliaries?

You should go for the reward experience the client order gives to you. The better the XP rewards for the player is, the more XP auxiliaries gets too. The required level of the CO has nothing to do with the XP rewards of auxiliaries.

Gotcha! Thanks!

Also, Boss Fight COs tend to fail a whole lot even with 12-star units and 13-star weapons so I feel I shouldn't ever do Boss Fight procurement orders for my Aux.

I was hamstrung as far as XP gains for my Aux because I wrongly assumed level req was more important than XP reward, but now I know better.

I find that the best COs to level your Aux are Kressida's. She has several that start at 30,000 EXP and require 30 of an item to be collected, so the success rate tends to be better (though they may need to be unlocked first, and their cooldown is a week); as long as you don't turn the COs in, you can just keep sending your Aux out for them continuously and rack up the EXP.