Here's some stuff I learned..
With a router table based dovetail system (Incra and Jointech), you have to plane the wood down to a specific thickness. This may or may not be a limitation.
I bought a used Woodrat a while ago. I haven't set it up yet, but you can do arbitrary thickness and spacing.. There are no templates, which is both good and bad. Another advantage of the woodrat is that it is awesome at making sliding dovetails. Also, you can climb cut (run the router the "wrong" way), since the wood is clamped down. This reduces tearout. Those latter two reasons were my main reason for buying the woodrat.
You may want to wait for the new Router Boss as well if you are going that direction. I don't think we are allowed to post links, so just do a serach.
I have no experience on the Liegh, PC or other traditional dovetail jigs, so I really can't compare those..