^ Is this the grande you were telling me about?
Some questions:
1) When looking at cores, I heard if the core does not have invincibility, it is not worth it. is this true?
2) What should I look for in artifacts?
Both of these questions stem from the fact I am a horder and I need to clean my storage out. But I have no desire to throw away a SoJ like item (from Diablo)!
1) It depends. Red raids for the most part require invulnerability on medkit cores.
For everything else, on a lot of heroes they can be extremely valuable but they aren't the only option and a core doesn't need that affix to be valuable. Some heroes may not want it at all.
Link some items in the SG chat and someone will tell you if it's a useful item I'm sure.
2) Damage rating relevant to your hero, skill points, crit chance are the staples. Some heroes need more from artifacts, like spirit sustain, health/invulnerability procs, attack speed.
More important is just building a hero you like and seeing what you start having problems with when you put them in harder content. If you were never in danger of dying or running out of spirit but it took a long time to kill something, sacrifice some of those things to replace with more damage.
Once again, if you're worried about selling something that is good, just link it into SG chat.