Hard to say…if it comes to just pick one for beginners and stand there with shield, spam some bombs or exist for healing - I would pick these:
Tank: Rein
DPS: Junkrat
Support: Lucio
We already have evidence from Blizzard that bronze/silver the highest picked support is not mercy/kiriko/ana form awhile back. Its Moira. The key trait Moira signifies is consistent damage that is not aim dependent while being difficult to solo due to strong self healing and an evasive kit.
Torbjorn is similar in that turret helps him counter evasive heroes due to the lack of aiming. His ability to literally 2v1 any encounter is pretty strong. He does have the +50 armor over other heroes. He has the overload ability to make him tougher over other heroes as well.
With his ranged spam he can take on long range heroes. With his bulk and fire power he can even duel tanks. Trying to hit a small/short hero with extra movement speed and up to 400hp in overload armor is kind of a bit much. On top of having to have closed any distance through spam or turret in the back.
Reinhardt and Soldier for tank and dps. Both are simple, easy to support and heavily overbuffed for marketing purposes.
For support its a bit complicated because in one hand Moira is easy value at her floor but you require to pick up the slack for having an overnerfed hero if you use her beyond Gold.
For tanks, I find that Orisa is pretty easy. I don’t play her to really say that she’s easy, but from observation she’s just so survivable that i feel like anyone can use her. For dps, i think Bastion is pretty easy. Just wait for turret and shred the tank. lastly for support, I think Brig is pretty easy. She just stays near vulnerable allies and gets pretty big value just by protecting them.
if we look at 3 things: Ease of use(how simple or complex the kit is), how mechanically intense they are, and how much gamesense you need to get value, then we get totally different answers. I will take the 3 from each role.
Tank: Zarya has the least complex kit, and rewards mechanics the best. Rein has 0 mechanical skill investment. Orissa has enough ignorant abillities that you dont need much game sense to get value, only decent supports.
DPS: Widow doesnt require game sense, and is simply point and click. Junkrat CAN aim, but doesnt need to, and reaper is the easiest if you have gamesense and nothing else.
Support. Just about every support is easy to use, even if badly. Bap beats out ana and illari for mechinics via AOE healing, and a 75 d/s primary. Moira and mercy are tied for easiest non-aim kit. Mercy is pure game sense, while moira is pure positioning. Moira isnt commital, so she can flank better that some DPS, and mercy has the survivability of a cockroach.
I play as Moira and will admit she has a wider level of entry compared to most supports.
There is a “right and wrong” way of playing a character. Being unable to figure it out will often see you out of position and punished for it. You can play Moira wrong and still have the means to correct your mistakes before you suffer heavy consequences. This is why she doesn’t have any tools to put her in line with the top picked supports. This however is a detriment to Moira as a skill disparity between her and the Opponent is often advantageous to her enemy.
that doesn’t mean Moira is the easiest, just that she’s more fun (and still easy). Nothing can get easier than mercy. No reload on healing/dmg boost. No aiming either. Very easy mobility. You can just attach yourself to a dps and get value from standing there. Literally don’t even have to touch your mouse or keyboard after you attach dmg boost. Nothing gets easier than that