Best at and power sets to experience all content 1-50 and beyond?

[Psyonico]

Willpower is a pretty smooth ride 1-50.  Its far from top of the game, bit it is smooth sailing.

 

I suspect psi armor would be as well.

[FlammeFatale]

My vote would go to crabbermind. I use mine as a badger.

 

I feel it is a solid all-rounder which is good at soloing but still brings buffs to parties.

The pets are fun and do not require micromanagement like a MM. 

It is not the tankiest character but is tanky enough (soft-capped positionnals + decent resistances).

It has excellent AoE damage. ST damage is lower yet sufficient for most purposes (AVs and GMs are do-able but take too long to be fun).