If you are eventually wanting to work in the US and get a green card, you should go for the RN. Otherwise, you will be leaving the country afterwards.
If you are going to go for training as an LPN, you would be using an F-1 visa and this requires sponsorship by a licensed school, not the hospital, unless it is a hospital-based program. At the end of your schooling you are permitted to work for a year for additonal training. LPNs are not fast tracked so you would not be able to complete your green card status change during that time and would have to leave the country,
You need to think in terms of what your final goals are.