Which of them do you think there will be more profit in?
It think it would be equality interesting and profitable to be a casino game developer, to be honest. It would be rather challenging at first, because how competitive the game market is, but if one come up with the right ideas, then it would be just matter of time before one's products start to get featured around on the internet and on several big casinos or high volume, with high enough volume then it would be just matter to keep up with support for those games and continue to offer new ideas for slots other casino games.
It would be also very tempting to be a casino owner, but the creativity part behing the development of games highly catches my attention.
In the worse case scenario, one develops a game and it does or get featured anywhere, which would be quite serious, depending on the budget used to develop one single game...