The upfront pricing was just an estimate of the total based on previous data. I much prefer it, because it incentivizes the driver to take the most efficient route, since they get paid based on arrival and not the way they go.

In the pay as you go system, you are at the mercy of the driver, and they are actually incentivized to take a longer route.

I've definitely had drivers take longer routes under the pay as you go system. I would complain to Uber and they would refund the money, but it was still a hassle to complain.