Do you have a house or apartment on the east coast or will you be truly living in it full time?
If it's just longer trips to the west coast, I would go with the smallest you can be comfortable in. Also keep in mind, it's a fun way to travel but long cross country hauls can be expensive in terms of gas. If the real reason is for a couple cross country runs per year, it's an expensive alternative.
Airstreams last because people pay for repairing them. They still have plenty of problems. It's almost a weird cult thing.. But really most are built the same way with the same appliances. None are intrinsically safer.
As others have mentioned, what truck do you have to tow with as that can really limit your options.
One other thought....how far north. It's pretty miserable living in an RV in cold snowy areas. It can be done but not fun.
