Ron - I think it's really important to identify your "real goal," and not to focus on intermediate or "proxy" goals like "signing up a lot of affiliates."
I assume that your "real goal" is to sell products or services, at a profit. In general, a commission-based affiliate program is ideally suited to this goal, because you ONLY pay affiliates who drive those sales, and you only pay them the amount you know you can afford (the commission percentage).
A commission-based program is somewhat "self-regulating," in that affiliates whose sites are clearly unrelated to your products are unlikely to join or drain your resources.
In contrast, a pay-per-click program tends to attract a lot of unscrupulous fraudsters, who may generate fraudulent traffic; it may also attract lots of low-quality affiliate web sites whose visitors have little or no purchase interest.
Choosing the rate to pay is often very difficult. In general, your "gross profit" margin will set the upper limit -- few merchants selling tangible products can afford commissions higher than 30%. However, you must also look at what your competitors (not just your direct competitors, but also non-competing merchants who may compete for your prospective affiliates' attention) are paying.
Commission amount is not the only factor that affiliates consider. Good affiliates will recognize that a 25% commission promise is worth very little if the merchant has a low conversion rate, or a low average transaction size.