How can I make my keyboard more responsive?
After checking this on a Samsung Galaxy S 3, a Nexus 7, and a Nexus 10, with several different keyboard apps, I couldn't see a similar issue, so I suspect this problem is specific to that model of phone. Perhaps HTC skimped on the touchscreen for this device, or did a poor job with the touchscreen integration. If that's it, there's probably nothing you can do but hope that a software update will fix the problem.

Alternatively, it could be a problem with that particular phone. Try giving the touchscreen a wipe with a damp cloth. Try to get access to another phone of the same model and check if it has the same problem: if it is only your phone, you should take it back to the shop and have them fix it.