I would just dive in. Each class has many defensive passives. Currently coming in at beta there is no true builds yet. Many of the skills are not in yet or are being reworked so at this point things are going to change over and over.
Also you can just play sentinel for now and choose the defensive passives.
I only played for about a week in the alpha, but I played a little bit of all of them and I like them all at least in the early stages. They seem to all have strengths from what I can tell and I didn’t feel any more powerful at least in the early goings between each of them.
Coming from a 49 year old gamer, I can honestly say that any class will work as noob friendly. I’ve tried a couple and this game really makes you feel heroic regardless of class which I love. You could almost say it’s a faceroll…I hate using that term but here it’s just really cool.
Any class easymodes the story content. Once you unlock your skills, lv them a bit and find some half decent gear the story content mobs are all 1-2 shot dead with bosses maybe few hits. With excellent gear and probably by lv30ish( when you have enough skill points to max out some passives/actives) you’re like god and instant killing everything in story content.
Nobody knows what beta is like but I wouldn’t stress what your first class is. Only advice I can give is if you know you want to play other classes keep gear you find for them, makes lving another character a lot easier when you have strong gear to give it from lv1.