Thats going to depend greatly on your budget and your needs. the socket is an AMD AM3 so here is a list of compatible processors for that chipset per http://www.findlaptopdriver.com/specs-hewlett-packard-3047h/
- Athlon II X2: 220
- Phenom II X2: B57, B59, B60
- Phenom II X3: B75, B77
- Phenom II X4: B95, B97, B99
as i said before its going to based of your needs and your budgest. if you are doing normal home/work use then it doesnt matter. if you game then the more you spend the more you get.