This is entirely up to you , i'd look through each of the clans and see which one you like best then build a deck with them , i suppose resuce is the cheapest clan to make a deck out of but it's your choice who you use , if you use rescue make sure you only buy resuce cos they work best as mono(just one clan ) deck. as for the others well just look for the one that interests you GG's
1st purchase credits so you can sell on the market and make money fast, 2nd look at the cards you've got and look at where they belong, 3rd sell some of your cards so you can buy what you need to make a deck.
for example: in a Danger Pack you've got:
at this pack, you can now make a Nightmare/Montana deck for ELO and Uppers/Montana deck for DT's(except, you still have to buy some expensive cards so you can play DT)
and on your 2nd pack, you choosed cool attitude and you've got:
(you are so lucky!!!)
you can now use Bangers as your main clan
What cards do you have now? Unless you plan on buying more credits I'd just go with the majority clan you have now. All have advantages and disadvantages and mostly it will depend on your style of play. Are you more of an aggressive or defensive player? Are you looking for a Type 1, 2, or ELO deck?
If aggressive then Rescue, Nightmare, GHEIST, Montana, & Bangers are my personal favorite clans. If defensive then Pussycats, Roots, & Montana are good to work with.
Most of the time it's best to mix two clans unless you're going with Rescue as OC-Luke mentioned.
I'd also check out the public presets for ideas and narrow your search to the type of game you want to play http://www.urban-rivals.com/presets/list.php