In general I would not suggest posting your projects on young freelance sites. Choose those at least 2-3 years old. Elder sites have bigger freelancers base (both webmasters and programmers), which leads to tough competition, better service, and lower prices.
I like
Scriptlance (it is online since 2001) more than others. I would say it is the best site for web project (quality/price). But it is not so good for non-web projects because freelance designers/programmers on Scriptlance are mostly web-oriented. They are doing well with server administration, html, php, perl, mysql, oscommerce, cubecart, and other popular web languages and web products.
Scriptlance also has a
certified member feature. Certified freelancers are usually more reliable than non-certified. This freelancers site gives you $1 signup bonus.
Additionally read article about
best freelance sites. All these sites are at least two years old, and all of them are respected sites.