This may be one of the most popular questions I see in VO forums on social media. New talents hear about these pay-to-play audition sites through other members of forums and blogs so generally, this question pops up weekly. So, what is the honest answer? The best website for VO gigs is your own!
P2P sites are not a bad way to get a few clients here and there but make sure you don't put all your eggs in this basket. Spend plenty of time marketing your own website. Get in touch with talent agents, production directors, eLearning companies and video production departments inside corporations. The potential client is likely getting calls or emails from other talents, but you're not necessarily competing with 300 other voice talents for one gig.
A successful voiceover business is built by starting relationships. And this is a result of direct marketing. In this day and age of VO, clients like working with a small talent pool. Especially video production directors inside large corporations. These working relationships are pure gold.
I have nothing against P2P sites. It's a decent place to start and you could easily book a few clients here and there but don't spend all day from sunrise to sunset doing nothing but auditioning on them. You're wasting a large portion of your day spitting into a fan. Instead, spend most of your day on direct marketing. 75% of my annual income comes from clients who have booked me off my direct marketing efforts. It works!