I enjoy most of the Penances as they generally encourage a different play style, or accomplishment.
Everyshot counts - wants you to use a weapon with a low ammo economy like the plasma gun
On overwatch - play a full sniper build and support your team by ripping apart elites from the squad’s backline.
There is nothing but the abyss… - a berserker play style where when faced with danger you fight harder
Friends will be friends - a bodyguard style where you protect your teammates at all costs.
You get the point.
Most challenges can be done fairly easily by simply changing your loadout and play style without hurting the overall effectiveness of the team. Then there is “out with a bang” a penance that tells the player to blow themselves over and over until they happen to kill 3 elites.
Down yourself in the middle of fight in hopes that the tiny aoe of 600 damage ( at maximum ramp up with 4 warp charges) kills those three elites mmmm yeah I’m not sure what play style this encourages unless your cosplaying a pox bomber