Do I have a better chance at getting into a highly selective school if I apply early decision?
Yes, but how much of a boost you get is very dependent on the specific circumstances.
Check out the “Is EA/ED a death trap?” thread.
Higher percentage of the applicants for EA/ED are accepted compared to their counterpart during the RD round. HOWEVER, (elite) schools attribute this fact towards the simple calibers of the early applicants – the stronger, more well-rounded and specially talented group of people apply early round, hence the higher acceptance rate.
The general advice is this: if you feel your application is solid in all aspects - GPA, SAT/ACT, subject tests, ECs and awards etc - apply early. If not, wait until the regular round.