There are deadly bacteria (e.g Mycobacterium tuberculosis) and deadly viruses (e.g Ebola). So it is hard to say one is more dangerous than the other. Also different viruses and bacteria will cause different levels of infection depending on the age, living conditions and even race of those infected.
One could argue that there are beneficial bacteria that can actually help us (e.g the bacteria that live in your intestines have a positive effect on your immune system). As far as I know there are not any viruses that are able to perform the same function.
However, lots of our DNA originally started out as viral DNA. I think that there is more foreign DNA that incorporated itself into our genome than our own. A lot of this DNA has been described as ‘junk DNA’ but as we examine it more and more it turns out that it is there for a reason (e.g structural stability). So in some respects it is also providing a benefit to us.
Personally I think that because a lot of bacterial infections can be treated with antibiotics and viruses cannot I would pick virus over bacteria as more dangerous, but only just 😀
As Peter has said – there are really dangerous bacteria and really dangerous viruses. I’d pick viruses as slightly worse for the same reason as Peter – because they can’t be treated with antibiotics. However, as more bacteria become antibiotic resistant treating them might get a lot harder.