It's been very long since I've played Gold. During the first, I thought it was just Attract that's the problem, but then I've lost my Quilava against that Miltank.
If the rumors are true, then Normal type Pokemon are the strongest. Of course with a fighting Pokemon, you would have ease, but against a Miltank, it's hard to take it down with high stamina and strength.
To beat Miltank, make sure to have a female Pokemon to help you to avoid attract. If one of your Pokemon ends up in love, switch to another Pokemon. Don't go with a flying type or a fire type. Flaffy is good, but make sure Flaffy is strong and fast. It's fine when its paralyzed, just switch in time before you get crushed.
When Miltank is stuck paralyzed, and you can lucky, finish Miltank off for good.
I am Red, Knights of the Pokemon Round Table. I have come afar to bring justice to all warriors and trainers with my valiant Pokemon and my weapon.