One of the most prominent evolutions in Mass Effect has been its combat. With each entry it gets a bit more refined, a bit deeper and, for better or worse, more action-packed. It's speedy, punchy and about moment-to-moment decisions more than it is a grand strategy. It gets even more interesting depending on which class you pick.
In the Legendary Edition, classes have been given some small reworkings. In the first Mass Effect, weapons are no longer locked to your class, having proficiencies instead, opening up even more possibilities across the trilogy. As such, it also gets a little easier to give a more definitive listing of the whole trilogy, too.
6 Engineer
I know, Engineer always ends up on the bottom, but it's for a reason! It's not an inherently bad class as its Tech abilities actually have lots of good aspects, but the dual capabilities of other classes tend to outshine it. The Engineer is all about staying in cover and providing assistance, letting your allies keep you safe while you provide back-up.
Being an engineer means being the one who has to take a slower approach and keep enemies on their toes, but as a result, you can't really handle direct combat. The loosened weapon restrictions make the class a bit more viable from the original pistols restriction, but it's not enough to elevate it. It doesn't grow much farther in later entries either, though it does finally get some spotlight in the Omega DLC, for the few Engineers out there.
5 Adept
The second of Mass Effect's three class classifications are Biotics. Biotics are like Mass Effect's version of magic, with individuals manipulating Mass Effect Fields to distort space around them. Adepts fall into something similar to Engineer, originally relying on lighter weapons and being low in health, but Adept's abilities at least allow you to be a more active participant.
Adepts can create a barrier for themselves and whip enemies out of cover with their abilities. Similarly to Engineers, they lack the versatility of other classes and need to rely heavily on squadmates, but who doesn't love running around as a fearsome space mage whipping enemies with your mind?
4 Infiltrator
Infiltrators are a fun class that open up a quite different way to play the game. They're a mix of Tech and Combat but, unlike the others, the Infiltrator is all about stealth making you the rogue of the party. They're not as buff as Soldiers but at least they can still get medium armor too.
In Mass Effect 1, they can pick people off at a distance with Snipers, while still being able to survive up close with sturdier armor and other offensive abilities. And in Mass Effect 2 and 3, you can even turn invisible to get behind enemy lines. It offers mobility and the power to be effective both up-close and at range. It requires skill to use effectively, but it's a rewarding playstyle that makes you feel like you control the battlefield.
3 Soldier
The third of the basic classes, Soldier is the combat specialist. They're the jack of all trades for weapons and a tank when you need them to be. . They're proficient in just about every weapon and are the only class that can wear heavy armor, and they can take just as much as they can deal. Despite all they have going for them, they're just an incredibly boring choice.
They lack the flair of Biotics and the tactics of Tech but can accomplish any task. So it doesn't matter that they're boring, because they work damn well. On top of that, they get an almost bullet-time slowdown in later games that let you get pinpoint aiming. Sometimes, basic is all you need to get the job done.
2 Sentinel
Sentinels are a mix of Tech and Biotics and a powerhouse to boot that only gets stronger with each game. Sentinels lack the creativity of an Adept's biotics, relying more on practical things like enemy grouping and barrier-busting than flinging people like ragdolls, but they can also get right up in your face with a shield that unleashes a blast when broken.
They can get medium armor too and, by Mass Effect 3, have proficiencies in most weapons, meaning they can keep themselves safe up close as well. Of course, they have Tech abilities too and can easily freeze or overload anything Biotics don't obliterate. Overall, they've got great utility and let you more effectively cover all bases with less effort.
1 Vanguard
Now, although Vanguard may not be the greatest class for pure utility (that honor likely goes to Sentinels) the Vanguard's mix of Combat and Biotic abilities make it incredibly unique - the Biotic Charge. Unique to Vanguards, Biotic Charge allows you to target any enemy and dash at them, dealing a great deal of damage and causing a small amount of knockback, allowing you to immediately follow up with a shotgun.
Vanguards can also get medium armor to keep themselves alive longer, but have enough Biotic abilities to knock away enemies that prove a threat. They're not quite weak enough to be a glass cannon but not strong enough to be a juggernaut, acting as a happy middle between the two.