If you had to make the ultimate late game army out of 1 or 2 types of units, what would those be?

I'm playing with a big group of friends, and we all suck so bad that there's no such thing as an early game rush at all, and games extend to 1-2 hours every single time.

It's pretty awesome tbh, the other day I somehow won a match with an army of 60+ colossi, and watching them destroy everything while barely taking any losses was hilarious. But I'm gonna catch a ton of shit if I ever try to pull that off again and I've no idea what even makes a good late game unit, so what's next?