Go for the Magicka Necromancer build first, build it towards doing decent enough damage that you don't feel carried in veteran dungeon content. This way you will learn how to heal properly, too, since efficient healing is very similar to efficient damage parsing, for when you want to build healers later on. This is where you will get the most experience in the shortest time out of the two options you gave.

Also playing as a Damage Dealer in dungeons helps you understand what efficient healing versus inefficient healing looks and feels like, what efficient tanking versus inefficient tanking looks and feels like, and you will learn by observing what sort of playstyles works for the greater good of the group, and what sort of playstyles force everyone else to work that much harder to clear the content.

Also, just realised you didn't specify whether you want to play PVE or PVP, the answer above is tailored towards the assumption you meant for PVE.

Not exactly a 'general discussion' to be honest. My take is flip a coin. Heads go with tails, tails go with scales.

I’m always a Khajiit in all tes games but I picked Argonian for this poll because I didn’t like the eye patch

DKs are overpowered, oversimplified, and oversaturate Tamriel these days. Easy mode class.

MagCro is more challenging & unique. Has more opportunity for you to create your own build solutions & playing style. More room to grow and refine your toon in a more original & distinctive way.