I'm a bit torn on 1st Gen. My favorite as a 7 year old was probably Charizard, but for all the times I've played FireRed or HeartGold, Dewgong is probably my favorite. He was the first pokemon I ever got to level 100 and I facerolled Lance and friends so hard with him. Would have said Slowbro, but I prefer Slowking.
Plus he's adorable.