What is the better way to speed up gameplay as the level rises?

I started with game programming couple of weeks back. For the starters I tried to develop ZigZag (link takes you to 2 min gameplay).

I am done with the logic of gameplay by now. It runs well and all. Now I want to speed up the gameplay as user passes some score. Say after 100 points increase the speed of the ball.

I have two options:

1. Control the speed using time-delay by varying time.delay(var).
2. Actually increasing the speed of the moving ball

Not sure which one is a good idea in long term, I’m looking for help from experienced game developers.

You can checkout the source code: https://github.com/ravi-ojha/zigway/blob/master/zigway.py