I've played both and I think t3 edges DM.
If you don't have to, I wouldn't buy either one.
Both games are repetitive.
T3 is more modern and has some appeal on the price but the backbox rpg gets lame quickly.
DM starts off lame and ends that way too IMO
If you like Sci-Fi themed pins then you might like Dr WHO. I think it would stay in a collection longer but other guys here might weigh in on that better who have more time in on that pin.