I don't think it really matters how new your site is as to whether your choose CPM, CPC (PPC), or even CPA - the choice is more about how much time and effort you are prepared to spend on making those ads convert.
The easiest way to compare the different options is through eCPM (effective cost per mille), which basically tells you how much you would likely earn from a thousand impressions taking into account the click through rate (CTR) for PPC and CPA ads, as well as the conversion rates for CPA ads - to give you an estimation.
The outline below are with regard to small/medium publishers - as if you are a premium publisher you can command much higher rates on a CPM basis either through private sales or premium representation.
CPM ads are the least effort on the part of the publisher as you are paid a set fee per thousand impressions no matter how many users click on them and how many of those convert into sales/actions for the advertiser. Because all the risk of conversion on these ads is with the advertiser, publishers tend to earn lower rates eCPMs, but you do just put the ads up and leave them alone.
PPC/CPC ads sit in the middle because the risk of users clicking the ads fall on the publisher - meaning it becomes in your interest to better place and promote those ads within your site. But how those users convert after the click remains with the advertiser. If you can generate a decent CTR with your site then you should be able to earn more through PPC/CPC as a small/medium publisher than via CPM.
CPA (affiliate) ads mean all the risk is left with the publisher as it is down to your to make sure users both click on those ads and then buy something or perform some other action on the advertiser's site. If you can make your users convert well then these can be the most lucrative, but they are by far the most work to promote.
Depending on the site and your motivations you should choose which method suits your particular needs better - there is no right or wrong answer.
Last edited by snakeair; 04-26-2012 at 09:18 PM.
Reason: self promoting not allowed