This was an Ace Double from 1961, combining a Robert Silverberg novel (expanded from an earlier version published in 1959) with the Leigh Brackett novel that won the 1945 Retro Hugo. Of the latter, I wrote at the time:

Second paragraph of third chapter:

Mayo McCall watched the men running back and forth below. Quite calmly she reached out and closed the switch that controlled her testing beam — the ray that spanned the head of the drift and checked every carload of dull red rock for Fallonite content, the chemically amorphous substance that was already beginning to revolutionize the Terran plastic industry.

Fairly standard but well executed pulp planetary romance / space opera, with desert Mars, swampy Venus and our hero overcoming evil Earth industrialists and perhaps a bit of commentary on colonialism as well. Brackett is one of two women in this category, and the only one to get a solo listing. You can get the original pulp version here and buy a later book version here.

The second paragraph of the third chapter of Collision Course is:

Bernard lay sprawled in his vibrochair, cradling a volume of Yeats on his lap while the shoulder-lamp wriggled unhappily in its attempt to keep the beam focussed on the page no matter how Bernard might alter his position. A flask of rare brandy, twenty years old, imported from one of the Procyon worlds, was within easy reach. Bernard had his drink, his music, his poetry, his warmth. What better way, he asked himself, to relax after spending two hours trying to pound the essentials of sociometrics into the heads of an obtuse clump of sophomores?

It’s early but very competent Silverberg, a new wrinkle on the Cosmic Duel theme where humanity and one group of aliens are competing for control of our galaxy and a godlike force intervenes to force a settlement. Particularly entertaining in that the humans in Team Earth don’t get on with each other at all. Needless to say, no women characters appear except in flashbacks.

You can get Collision Course separately here, and the Ace Double here.

This was the SF book that had lingered longest unread on my shelves. Next on that pile is Major Matt Mason: Moon Mission by George S. Elrick (if I can find it).