1, HKUST is a state university, so you will spend less time learning languages, which is more conducive to your faster integration into the study life in the United States. However, if Lavin is a private university, it will take longer to learn the language.
2. In terms of environment, Lavin is in California, and the environment is better. Colorado is not as good as California, but you also said that the learning atmosphere is more important, so it doesn't matter.
3. In terms of employment, HKUST State University will also be superior to Lavin. After all, HKUST ranks higher, and those who rank higher in employment will have an advantage, which is the case in China.
Finally, a warm reminder, you'd better take a language test, which will help you apply for a better school and don't waste too much time on language.
If you have any questions, please ask again. I hope you can adopt them.