1) Little advantage to dual side - once you get used to any system, it's instintive
2) About the same
3) Speedplay cleats do wear out faster and require much more attention/maintenance

The longer answer is you need to find out for yourself. Most cyclists end up changing/trying out multiple bike parts over time to find out what works best for them. If you're a newbie, it's a good idea to find a LBS that you know and trust. Listening to their advice and posting here for opinions gets you no where - you'll get advice all over the place