For simplicity you would be best off hosting it in one datacenter.
If the problem is speed, start with optimizing your existing code.
Since you running wordpress, look at the plugins your running. disable them all and turn them back on one by one. see how much of a difference the performance is. Use a caching plugin such as W3 Total Cache.
If that isn't enough consider a larger server. If your using shared hosting, get rid of that and move to a VPS. Slicehost and Linode are good options.
If you aren't comfortable running your own Server there are people out there who will run it for you. XenScale.com is one. (Full Discloser: I work for them)
If you traffic is such that you can't scale vertically (bigger hardware) you can scale horizontally (more servers) by setting up a cluster. This is pretty involved and not for the feint of heart but a good sysadmin can do this for you.