First, decide whether your main goal is to get PPC revenue or sell the domain. If a domain doesn't get much traffic at one parking site, it probably won't get any more at another one. Whether the little traffic you get acually clicks depends on a lot of things, including how well the parking site optimizes the traffic or allows you to customize the link keywords. SedoPro parking does allow you this control. Standard parking is pretty limited to a single keyword from what I remember. If your main goal is PPC revenue, then pick one that either has high click throughs, high payments per click, or allows you to customize and tweak the PPC links. Sometimes an affilliate page can pay more than a generic PPC parking page.
If your main goal is to sell the domain, they sedo, fabulous, or afternic are good choices because they show it's for sale on the parking page if you want, and list the domain in the for sale domains listings for those specifically looking to buy. In this case, revenue is good and helps pay the renewals, but probably shouldn't be the primary reason for picking the parking site.
Most of my domains were registered for development potential rather than type-in potential. Therefore, to me PPC is just a bonus, and I make my real revenue from sales of domains.
