What kind of work do you use elance for?
Elance is more “marketing” oriented (best term I can think of). Writing, web design, copy, etc.
Rentacoder is more hardcore technical, coding obviously being the main thing.
I’ve used Rentacoder, it’s excellent in terms of establishing a safe biz relationship. Sometimes you’ll choose the wrong person, but it’s recoverable (e.g., language difficulties). The signup process is a bit involved, and you probably will want to establish a PayPal account before you start (PayPal is the main medium of exchange on Rentacoder). It has a lot of options and protections for both sides of the deal.
I have not used Elance, but friends have with decent results. From what I can tell it’s very similar to Rentacoder in terms of helping with the business relationship. I wouldn’t hesitiate to try it for “soft” projects, including the artistic side of web design.