I would like to set your expectation level on the lower end of the scale. If this is your scale:
High-------------------------------------Low
United------------------------------Northwest
----------------------------TWA-------------
I think TWA lands somewhere there.
The food is not as good as United first class. I've had some great meals DEN-STL on United. However, TWA's 757's are fairly comfortable in first, and there will be entertainment. Your connecting times look good and St. Louis is actually a fairly easy connect. FA's can be anywhere from crotchedy and old to fun and old to fun and young to young and dumb but eager.