I take Amtrak quite a bit, and therefore credit all my ST mileage to CO. Continental miles transfers 1:1 in 5000-mile increments to Amtrak Guest Rewards points. For 24,000 AGR points, I can get 4 of my typical NE Corridor round trips, worth $700-1000 (or triple the value I'd derive from a 25,000 mile domestic airline RT).

You rightly dismiss a sweeping generalization, then make one of your own. There are many reasons why people may prefer UA over NW and vice versa depending on their situation and priorities (e.g. NW's route network doesn't work for me). And you'll find many on the UA board, myself included, strongly prefer the certificate system as both more equitable to elites across tiers and more protective of the premium cabin.