From the street these towers look like the same decision: two newer 41-story Denny Triangle high-rises with skyline views and amenities stacked toward the top. They are not the same decision. The differences that matter are unit count, the resale competition that comes with it, the developer track record, and how each specific unit is positioned in its stack.
Nexus gives you the larger building, the lower published entry price, and the tech-forward package, at the cost of more in-building resale competition. Spire gives you the newest construction and a tighter unit count, at a slightly higher entry point. Neither wins on the amenity list alone. The better-positioned unit in either tower beats the weaker unit in the other, every time.
Before you choose, I put the two specific units side by side on view orientation, floor height, monthly cost per square foot, parking, and the current HOA reserve and assessment position. That comparison, not the marketing, is what tells you which building is actually the better buy for you.