Can't speak to ME1 since the system was so vastly different, but for ME2 and 3, Sentinal and Straight up Biotic were safe options, just much more tedious particularly once you up the difficulty. Vanguard was pretty much a face roll in both games, up until the 6 Banshee bullshit right before the end of ME3 because of the ridiculous sync kill vacuum reach. If you were good at the game, infiltrator and techies were pretty damn amazing. In ME2 especially a sniper infiltrator is pretty godlike if you can line up headshots consistently, especially on the final boss in that game. ME3 just had a few fights where stealthing and positioning were impossible but I remember my Infiltrator playthrough being pretty effortless on Nightmare the last time I ran through ME3. Shotgun Tech was fun, but it is a ton of waiting on cooldowns. Lot of good story shortcuts for the techie though (forget the name of the class). I think if you just want to be all around versitile and good, Sentinal gives you tons of options.
