John Collins is the whiskey brother to Tom Collins. I realize there is also a Whiskey Collins, but the Collins is such an Irish-American cocktail that it needs doing with a real Irish whiskey.
I'm hot and cold on my feelings about Donegal Estates whiskey. It is dry and almost flavorless except for a bit of grain on the center of the tongue. This makes it excellent as a cocktail whiskey with light and refreshing drinks like the Collins. It is uninteresting when taken neat, except that occasionally it pairs well with shortbread or as a topper to fizzy drinks. For me, it wasn't worth the price, in the 30 dollar range, but that's the thing about Irish whiskey imports. You pay a premium regardless of quality.