Workplace benefits I can't comment because I haven't been to either's offices.

Career progression I suppose would follow the normal uni grad civil servant trajectory lor. Asst Dir, Dy Dir by the time you retire if you're lucky.

I did my ns at Mindef Building and as a now as a civilian guy going back there now to work I will totally hate it because of the oppressive memories I have of that place. Nonetheless I wasn't involved in the daily project research gritty work that the DXOs do so I can't say much. But environment wise.. Mindef is pretty out of the way if you stay in the east and its nowhere near any MRT station. Majorly hard to come to work everyday taking the bus all the time. And the building is damn old fyi.