Get both. Go to a bonsai nursery and talk to the people and figure out what are good species for beginner in your climate. In Spring (around now in the Northern Hemisphere...) you can try to dig up some seedlings or young trees and put them in a pot. Learning the art of bonsai usually involves some casualties, so it's better to have multiple trees. Also, having multiple trees at different developmental stages gives you a better overview of what to do with the younger trees when they mature.
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