If you buy 420 credits, then, with that 420 credits, you can either buy the titanium pack and get 30 characters FROM 4 CLANS with 4 RARES GUARANTEED and have 125 credits left for other things, or, you can buy 8 Full Decks, get 64 characters FROM ALL CLANS, and have 8 RARES GUARANTEED, and have 20 credits left over to buy one of the 20 credit packs.
The Titanium pack is for people who have a lot of cards and want to limit their results to the clans they lack.
Currently NB packs always gives you better avg clintz per credit due to the inflation of new cards for their missions.
Nevertheless, somehow i still prefer opening up titanium packs compared to NB packs...
going with silvers like broken jaw is saying may net you more rares, but imho even when you're starting out it's better to get titanium packs so that you get structured decks compared the possible multitude of cards scattered among all the clans through silver.