wordpress is the worst - except for all the others. i think most people hate WP because, well, a bunch of reasons, but reason #1 is usually speed -- WP is super-slow if you don't host it well. so, find a blazing-fast WP host. your client will be like, 'ok'.
In the past year, every WP website my company did became too slow, even I noticed it when using admin panel for adding new features, I mean it's barely usable, constantly throwing 404 errors.
Also, the clients started complaining heavily, but I'm unable to come up with the solution since on test server everything works perfectly. I also had some suspicious that's because of the bad host, because it effects every project done with WP, but the company owner claims differently since he's 'really good' at working with servers.