It seems to me that they were both very similar. Geta may get some good press because he was killed by his brother, who was thoroughly hated.

I know there is hardly any concrete source material on the younger Septimius but in my opinion, with the small difference in age between him and his brother and the circumstances following any murder of his brother, if it had been Geta who had survived 211CE then he would have turned out very similar if not identical as to how Caracalla ruled