James Rolfe / The AVGN. Loved him since the Power Glove episode (the first I ever saw). Hated Mike Matei from day one too. I still watch old AVGN episodes with relative frequency, and every single time there's a new one I watch it ASAP.
I've enjoyed Game Grumps for a long time. Started watching due to Arin (who I knew from his Newgrounds stuff) and liked JonTron as a result as well. Kept watching Jon stuff after the split and then, well, you know. Grew to love Dan very, very god damn fast on his own, unrelated to Jon's shenanigans. That said, I barely watch them anymore. Just from time to time nowadays.
Don't know if this counts but I watch a lot of Digital Foundry stuff and they're an invaluable team to me.
But the ones I watch the most nowadays, and it's not even close, in order:
Arlo. I don't even think he needs a description. He's a puppet, he's funny and he loves Nintendo.
Scott the Woz. Recent discovery, fucking love him and I hope to god he doesn't end up like so many gaming personalities. You know what I'm talking about.
Jim Fucking Sterling son. Thank God for him, don't think I need to say anything else.
I don't expect literally anything in this list to age well. Nobody's safe.