I usually suggest Rosys over Balls to beginners at the pet store where I work, mostly because they don't have the humidity needs and don't go off feed as often. They also stay smaller overall. I would say go hold at least one snake of each type and see which you like about them though. Also think about cage size, a Rosy can stay in a 20L but most Ball pythons will outgrow that. Good luck on your first snake!
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Danne
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1.0 BRB "Monroe"
1.1 Leos "Bowser & Peach"
0.3 cats "Beast, Smokey & Thelma"
0.4.2 fish