Ah now everyone will give there own fave here Stew(my dogs called Stewie! sorry that has nothing to do with anything does it!)
I like Bansko it is the largest and highest of the resorts and also is a town in its own right, so loads of restaurants and bars. Pamporovo is much smaller but still nice and has very lively nightlife. Borovets seems to be the party place.
Stew, the most runs are to be found in Bansko and probably also edges it with the snow record. As far as nightlife is concerned, all resorts offer a pretty decent level with bars clubs and resturants for all tastes.
March (hopefully) will see all resorts with a good covering of snow but the last 2 years have proved to be a disappointment compared to previous years.
By the sounds of things - Bansko would suit you best (IMO)
Bansko. Especially as you are going in march. Was there in march last year and the snow was still good. At the same time pamps was a muddy mess and boro very limited due to thawing snow.
Thanks everyone, Bansko it is as we are going fairly late in the season as Damo says plus I had a dream I went skiing last night and it really was a hill of mud.
As budget is key as well it's Bulgaria all the way.