Have you thought of getting the starter pack? When i started with the popcorn roaster i was advised to get the starter pack. Its good as it gives you a variety of different beans from different contients. There is no one type of bean which would be better, though some of the beans i have found are easier to roast that others. A good start is the Peru ceja, thats what i have found anyway someone else may have a different view on it.
Good luck with it, its heaps of fun and addictive