It doesn't favor anything, it's random, with (i think) a modifier based what you already achieved: if you still have a lot of uncommon weapons to unlock/level up to X, you'd better stick with the veteran packs. Why?
Because the game will favor the weapons/mods you still didn't complete. This will result in spectre packs dropping uncommon weapons, thus wasting your credits. The strategy i used is this:
- you start leveling a char till level 16-17, when you're ready to do gold missions
- from level 1-16 you buy (vetearan) packs normally, completing your uncommon equipement
- wen you reach level 16 or 17, you can either move to gold and save all the money for when you promote your character, or just move onto another char till level 16 again
- when you promote your char(s) you'll have enough money to buy tons of veteran packs and level up your low-levels with the characters dropped (a neo promoted class will result in gaining up to 10 levels just buying packs, if you're lucky enough)
Do this untill you complete your uncommon armory, then move onto the spectre packs. This will result in fast N7-leveling, a lot of weapons and characters and most of all, no xp-money waste!
PS: i forgot to add that you can track all your equipement progress using Bioware's social website. This is exactly my profile and you can see my progress too! It's a useful tool to keep an eye on your drops! Hope my post helped