you usually get 50 xp for completing a mission (they need to be the ones who already have about 5 reviews and have got past the review stage). sometimes that number varies depending on the size of the mission. ive had odd things where ive gotten 42 or 53 points before for some reason.
you can take the daily that if you complete 3 foundry missions you get more xp and a choice of a random item or some badges/emblems. the amount of xp scales with your level
you will level much slower with the foundry than cryptic missions but you will still get xp.
fire and steel, level 41 i think its called which was pretty awesome.
or you could try mine. 'crouching ty'gokor hidden demon' level 31 (there are two versions. one was sent over by Q from tribble, but it has some errors that i cant clean up. or the version i redesigned, but its still in the review stage that i could use some feedback on).
then it sequel, the hunter killer, level 41 which people seem to be really enjoying so far.