A proper set of road clipless pedals makes a big difference (I have found) to your ride.. so much so, that I hate using SPD’s on my road bikes now.
TBH there’s not much difference between Shimano and Look clipless systems, I’ve used both interchangeably for years. Agree with the post earlier saying just buy a cheap or mid-priced set, as you really don’t seem to get much performance benefit from the more expensive pedals.
Have not used Speedplays but they’re marketing themselves heavily and sponsoring several pro teams in 2013… could be good, but then there’s nothing wrong with the large/wide pedal interface that you get from Shimano or Look.
I currently use Shimano Ultegra. Approx £60.