It's not an easy choice, but I'd go with Milner.
To win the title, we need to beat City. To beat City, we need to play at our best. Which means doing all the things we're good at. High-line, pressing high and through the center, attacking overloads in the wide areas.
We can't do that without two full-backs pushing high. Milner is the best bet at mirroring Trent's attacking patterns, and is of course a very competent crosser.
Gomez struggles going forward. He doesn't have the technique to link up on the overloads and is a bad crosser.
Now of course the trouble with Milner is that his recovery pace is very bad these days, and we'd be susceptible to the ball behind him all game, but that's just a risk we'll have to live with I suppose.
Klopp rarely takes half measures, and I can't see him doing it for this game. Whenever we do beat City, it's when we out-press and outgun them. We can't win playing defensively against them anyway - Klopp's never done that.