Anywhere - I use Tide powder, non HE b/c we have old machines. I've used Free & Clear, and Original. Both have worked awesomely!
I used to buy Nellies as it was a "natural" cleaner, and I also used to only use 1/2 the amount. Since ditching that system my dipes have been so much cleaner - no stinkies and no buildup (I just always include an extra rinse).