I have played both and preferred mass effect overall. Both have in my opinion unsatisfying endings but I found Deus Ex to be worse when it came to the end was very disappointed.
Mass effect if you have played the first two and have a save to import is a richer game on a whole due to references and things you notice and characters from the previous two games.
Deus Ex has good solid gameplay, fun stealth and terrible boss fights, the story is pretty good as well but I found the conclusion very unsatisfying overall. Playing the dlc atm as I got it on sale and it's really fun to play again and sneak about in pipes.
Mass effect if you have played the first two and have a save to import is a richer game on a whole due to references and things you notice and characters from the previous two games.
Deus Ex has good solid gameplay, fun stealth and terrible boss fights, the story is pretty good as well but I found the conclusion very unsatisfying overall. Playing the dlc atm as I got it on sale and it's really fun to play again and sneak about in pipes.