It's very important that, not only the system you are willing to use is important, but also the transfer to this system. How much URLs we are talking about? 1000, 10000 - 1.000.000 ? Wordpress might get heavy and might need a special setup for high volume content sites, or high traffic sites. Changing the system is a huge risk that should be evaluated before doing the change. Remember to keep track of each single URL and redirect accordingly to the new URLs with a 301 in case the URLs really HAVE to change.

Hey, well i think that ADwords got very complex and that you should definelty consult with an expert before. The question is: How much budget are you willing to invest, what's your margin or customer lifetime and what would be you maximum CPA (Cost per acquisition)? In order to be able to estimate your budgets it would also be necessary to know your current conversion rate Visits > Sales.