I did a hub on how to learn to ride a motorcycle if you want good advice in which I suggest you go quad biking first. 1. to see if you like bikes and 2. to get used to bike controls. Any which way you decide to go I would suggest taking lessons from professional bikers as every bike is different and unlike cars there are bikes that you will not be able to ride even though you may want to. That said, unlike me, if you are tall with long legs this list of bikes won't be very long.
Take the sensible approach and enjoy years of incident free biking. Live to ride as some say,