I've always liked the challenge of soloing dungeons (of course some are not possible due to mechanics). What classes/builds will allow me to solo the largest amount of content?
I take a pet sorcerer, with the Volatile Familiar and Twilight Matriarch. Reasons include but are not limited to:
Excellent burst heal.
Excellent ticking heal (Critical Surge).
Pets that commonly tank one attacker for you.
Very good single-target ultimate skill (Greater Atronach).
Slightly better shield than other magicka classes (Empowered Ward is a little more forgiving than the 6-second shields).
DoTs that work even if you're busy trying to survive (pet basic attacks).
Skill bar space is distressingly tight, but that's the main drawback.
Nightblades excel at trash fights, because of the many on-kill bonuses, but they're nothing special against bosses.
I struggle surprisingly often with magicka templars. Probably I rely too much on Puncturing Sweeps and hence run into trouble when it doesn't fit well.
I've had some recent success with a magicka warden. Damage is really nice, in my opinion, as the Animal Companions skill line works quite well now. Strong HoTs plus Dampen Magicka can make up for the lack of a burst heal. And they're the other class with a pet who can tank some aggro.
Any class can be set up well for solo play, but Wardens and Necromancers have cheap purge skills that other classes don’t have. Necromancer also has an automatic chain skill built into their mitigation buff that can make solo play significantly more efficient.