Both anivia and vlad are really good.
Anivia is a really good comboer, but very easily squished. Her egg can be really helpful, but over very hard to play especially the placement of her wall. If Anivia's wall is placed too early ppl can get away, and that doesnt really help. Need to be careful especially where you place yourself because if you're in the wrong spot at the wrong time you can go down REAL fast.
Vlad is a little more forigiving I'd say. He has one of the best escaping skills b/c he can't be targeted while using it. Vlad can be a really good carry. He overall has really good skills that do really good damage. Vlad can be aggressive, and doesn't need to worry too much about dying really fast in team fights. Plus Vlad can tower dive to get kills and escape with his Sanguine pool D: I was playing koggy wen one vlad did that to me...=not a very happy kog'maw
It's a hard pick, but I'd choose Vlad :P Depends on your game style.