CA Zephyr is the better choice for scenery if it sticks to the schedule. I don't think you'll be disappointed. First day out of Chicago is large open fields of Midwestern USA, but then grab a seat in the Sightseer Lounge Car while the train is at Denver Union Station, as you'll want to be seated there as the train ascends through the Rockies for the entire day to Salt Lake City. Next day - again - head to the Sightseer Lounge (before or at Reno if relatively on-time), and get a seat for travelling over the Sierra Nevada mountains. Getting a seat in the Superliner Sightseer Lounge by the time you depart Denver and Reno (Westbound) is KEY! You'll break for lunch in the Diner, but should be able to find seats afterwards in the Superliner Sightseer Lounge. Course, the train is also down in its capacity (no second or third sleeper, no third coach, etc.), so it may be less demanding in the Superliner Sightseer Lounge Car.
When getting a roomette, I recommend the "upper deck" rooms 3 through 8 are typically the best in the regular Superliner Sleeper. Room 2 is ok - but closer to the bathroom and could be a bit disturbing, but definitely doable. Roomettes 9 and 10 are next to the door that goes to the adjacent Superliner passenger car (and more overtop of the trucks - wheels). I've always been OK with roomettes 9 and 10, but some people have it lower on their preference. Not a fan of the lower level sleepers (rooms 11 through 14), but if there's no other space available, I am sure it will do the the trick. If you are assigned roomettes 17 and above, you'll be in the Superliner Trans-Dorm Sleeper (crew sleeper). Again, I don't have an issue being here, but some do. CA Zephyr is a hard train to book a "through sleeper" on - from Chicago "all the way" to Emeryville. I'd still take whatever roomette you can get, as the scenery is worth it, and you'll largely be between the Diner and Sightseer Lounge during the day, then roomette for sleeping at night. Just bring earphones or something to block out the train horn and noise as needed.
When booking sleeper space, I always talk to an agent via phone. I am sure they hate me by the time I book my trips due to looking at options and trying to get the bedroom or roomette space I want. But they charge enough, so why not get what I want/prefer if possible. As I've gotten older - for the longer trips (two nights or two full day trips) I've been booking a bedroom if I can get it! But if travelling solo, roomette is certainly doable. Two people in a roomette - can be a bit challenging, especially with age.........
Happy travelling!!!