Depends on what you mean by "big" contract?
Also, are you UK or US based?

These questions will help you decide if the VC route is the right route and as the other commentator notes, speaking to a bank wouldn't be a bad idea either, although you may find you don't have the collateral to put up to support a loan. VC's also bring other value beyond money, if you get the right one.

Angels are a better route, depending on the amount of money you want/need. That should be informed by your cashflow projections to deliver the contract and the overall strategy of the business. Angelist is an option, though if you're not experienced raising you'll probably want someone trustworthy as a non-exec, consultant or advisor, to help you shape the proposition and help manage the raise.

So in short there are a lot of moving parts to answer this question.

A pitch deck is a must however, if for no other reason than to make clear in your own mind your immediate plans going forward. This is a good a template as any, to work from www.sequoiacap.com/ideas