Not a fan of Titanium pack, but I'd say Berzerk, Frozn, Vortex, and most likely Nightmare. This is so you can pick up all the nice rares from the newer clans and sell for a decent profit, there are multiple expensive rares and a small amount of cards, so it should be a good deal.

Wait until a new blood release, and buy 15 of those

I would personally buy elite packs and select Frozn, Berzerk, Vortex and Nightmare or new blood next friday if you want the new cards.

Grace, abnormal, and aaabat has given you good advice. http://urdb.kirlad.net/packs.php would support their suggestions.
if you're looking for the best "usable" cards per credits then you'd probably better off staying with new bloods (especially since they've added that DT incentive to play standard)

Nevertheless, i personally swear by titanium packs. I find that it's the best way to build up collection. You do have to live with the possibility of ending up with useless cards, but hey' it's a card collecting game and it's worth it (at least for me personally) to choose the clans where you still have 0/xx cards or less than 50% of any clan. Saving up for 300 credits from doing DTs and ELO also makes it more "rewarding". However, if what you want is best moneh or Hax cards per credits, then go with newbloods or elites.

Sentinel for Coby and Copper?