They're both good. I prefer
Tobias to
Tobiah though. I prefer your prn. to the
German one... It's not overdone in N.Am. and that's a point in its favour for sure...
Toby's ok as a nn... I think I've met 1 boy named
Toby and know of a singer/former rapper named
Toby (not sure if either was short for
Tobias)... and I believe I've known 2 girls named Tobi, which is kinda cool.