Depends imho - what are you looking for? more rares? more cards? most card value per credits?
i tend to stick with titanium 295 creds, but i guess newbloods tend to get you the most money ever since standard kicked in along with the newblood missions.
no experience with silver/gold/ultimate, but for rares i reckon ultimate gives more than the others.
Idk new bloods really are gr8t cause of friday releases but I always seem to get great pulls from classic. I got a zatman and Kenny out of one pack once and ive also got other great cards as well such as Hawk and Charlie out of some packs. It really depends on what you want but I normally tend to go with classic cause they are awesome for getting those cards that tend to go Cr.