Why does the Messages.app alert me to new messages quicker than my actual iPhone?
As you are active on your compy, it gives you first opportunity to answer from there. Only if you don't bring Messages to the front does it then ping the phone.

Personally, I like it - I can type a heck of a lot faster with 8 fingers than 2 thumbs ;)

&amp; now it can do SMS too, fabulous.

BTW, if you don't like it, I've never seen any option to change that behaviour. It may auto-switch if you start answering on the phone instead, but I haven't specifically checked for if it does that.