Superskinny. BUT even though I would definately rather put on a few stone rather than lose five times that amount, people still underestimate how hard it is to gain weight, even in a healthy eay. Think about how rubbish you feel after you've eaten more than you're used too/had a 'fat' day, now imagine feeling like that every day until you've reached your target weight. Not fun! Deliberately gaining weight is something that feels totally unnatural.
Also, people tend to be tougher to your face about being thin - I used to struggle to understand why my friends were so persistent about getting me to eat more and making me feel really uncomfortable,yet it would have been totally unacceptable for them to tell one of my overweight friends to make some basic food swaps. Now I know the reasons are pretty obvious, but still it wasn't pleasant.
Having said all this, I would stil rather be superskinny because it does seem to be that it is more socially acceptable. Undereating disorders are treated with way more sympathy than overeating disorders which isn't really fair.