Which beginner bike a rider should buy would depend, to a certain extent, on the personality and level of responsibility of the rider. I've known folks that could have ridden 600cc sportbikes as their first bikes-- but I'm not one of them.
If I had it to do all over again, and started riding today, I'd want to ride a used GS500E. Cheap as dirt to purchase, I'd be able to resell it for cost (if I ever wanted to), it's light, simple, free of plastic bodywork, and it's a 500cc twin. As a beginner, I like middleweight twins because they put out broad, tractable power. They don't need to be revved to give fairly lively acceleration.
Avoiding the big depreciation hit, especially when I drop it, will help keep some cash in my pocket for when I stepped up from the GS500E to the Hayabusa turbo...