Which shard or shards do you think are the most useful to a sorcerer on average? Which ones do you think would have the most impact on a character over a campaign?

I am playing a sorcerer who uses primarily save-or-suck spells and I am fiending to get my hands on the shadowfell shard. It effectively allows my character to spend 1 point and get the effects of Subtle/Distant/Careful, which I use to affect the spell, a better Hightened (which normally cost 3 and only lasts for that spell instead of a full round possibly aiding other casters), and a situational ability score disadvantage similar to the Hex spell. Spend 1 sorcery point and get 4 points of effects plus a little.

 EDIT: changed empowered to heightened because Stratoburn brought it to my attention.

Shadowfell shard would add the Heightened spell affect, not the Empowered one.  Plus half of a one-round hex spell. 

If you do use save-or-suck spells, then yea that shard sounds like the best option.  Disadvantage is really powerful, and that has the potential to make bosses burn through their legendary actions pretty quickly. 

Did you dip into any other classes for better armor and a shield?  Landing the spell is great, but if the bad guys know that you are the one casting, they may target you more.  Casting something cool and then losing concentration on the next turn can really suck.                

Draconic Sorcerer X, Great Old One Warlock (Chain) 3

I know, it is like I chose the everyone's least favorite sub-classes to mix together and focused on some of the most difficult types of spells to use. I have been focusing on intelligence and charisma save spells for when I can, but built an interesting support character. My group picked up an Animated Shield and my GM allowed me to benefit from it which helped my AC.