Which mass effect class?

ok so i want my character to play like i would in a real-life situation... i don't like rushing to things or attacking head on. i usually follow my own little group but i am not the leader. and in paintball i am usually one of the last to be taken out because i am hardly noticed lol. i am usually 2nd to last to get out. i was thinking either adept, infiltrator, or sentinel? can someone help and explain the roles of each of these classes in real-life and which is most like me? thx :)