well for me being under weight is better but i also am anerexic
The belief that you have to be one or the other, either overweight or underweight is part of your eating disorder. It's an error in thinking that comes with the territory. If you eat healthy for your age, activity level and metabolism, your weight should stay steady with only a couple pound natural variation. If you get help for your eating disorder one of the things that will change is this fear that you will always either have to work on restricting and losing weight or you will gain weight in an uncontrolled manner. It just isn't so.
*being underweight is safer.
There are many people considered underweight (with a BMI of 18 or under) who are perfectly healthy, and just happen to have speedier metabolisms or live super active lifestyles. If you're comparing it to 50 pounds of excess weight, then being underweight is a safer.
It's normal to fluctuate 5-10 pounds every couple of months (excluding prementrual water retention), but yo-yoing a lot more than that can be hard on your body. Consistency is best. Try to find a place where you're not restricting and not overeating, exersize 3-4 times a week and keep the stress levels as low as possible. You're body will find it's happy place.