I've actually thought about this question a lot. There are a lot of upsides to being a vampire, depending on the stories and different theories you find most believable. Heightened senses, perfect vision, heightened reflexes, quick healing. Some stories even bring in shapeshifting, mind control, mind reading! The possibilities could be endless! Not to mention you could never die from aging. That would appeal to those that are afraid of death, or growing old.
The only one I would really have a problem with is never dying. Sure, living forever could be great. But outliving everyone you know would be really sad. Eventually, it would get boring, I think. You also have to drink blood to stay alive, and based off of Nightlord eventually you have to kill someone to keep yourself alive. My conscience probably wouldn't handle that very well.
If I woke up a vampire, I would probably party. See how much alcohol it takes to get drunk, if getting drunk is even possible. I'd push the limits of my new abilities, depending on what I get. I think it would be fun for a while! But once I outlived my family, I'd find a way to die. I wouldn't like being alone like that.