Soul Gravy - Used to play hardcore. Then I also got into Arena. I finally gave all of it up due to the cost of staying current and because the cards and mechanics became ridiculously overpowered. Overall gameplay was sacrificed in the name of letting neck-bearded mouth-breathers orgasm over the latest 12/12 indestructable flying life-gaining draw-a-card-every-time-it-does-damage for four mana cost creatures.
When did you stop. What color was your go to?
Have any old valuable cards?
I stopped Arena a year or so ago, but I didn't consider myself playing seriously at that time. I hadn't played paper Magic in probably a few years prior to that. I usually play for a few years, lose interest and take a few years off, pick it back up, etc.
Way back when I played Sligh and Stasis, mostly. The deck I've ran most recently in a Grand Prix tournament (never placed) was mono red aggro.
I never had any truly valuable cards, but one of my best friends had two sets of the power nine. Yes, I got to play with them and yes, they made me better than everyone else in the room when I did. :P