If the 530i has a sport package, it will handle better than an xi. The xi's "sport package" doesn't have a tuned suspension the way the i does. So if you have a way to manage in snow, I'd say go for the RWD i. In my case, I need my car to have snow traction so I've owned AWD cars for years.
From what I understand from friends who own RWD BMWs, they are useless in the snow without snow tires, so be prepared for either snow tires or always using your truck in the snow.
The xi simply has more bits and pieces that could potentially break. Any time you have more parts, you have more stuff that can break.
These are just some random thoughts on my part. Hopefully others will add more useful posts.