What types of star do we know are hostile to life (like ours)? Certainly all stars have enough energy for a planet to host life. But a more magnetically active star is not preferred because solar ejection could strip planets of their atmosphere. What's the right balance?

Which stellar category of a star is suitable for hosting life excluding G2V class (our Sun's category)?
We so far have a sample size of 1. We know that a largish star, with a surface temperature at about 4.5 billion years of 5800K can be stable enough to support life for long enough for intelligence to evolve. We are fairly sure that very large stars don't last long enough. 

With only one data point to extrapolate there is a tendency to think that stars that are like the sun offer the best environment for life. We are fairly sure that very large stars don't last long enough. It seems reasonable to exclude highly variable stars, or ones whose outbursts would strip the atmosphere from any planet. Intuitively these would seem to be less likely sites for life. But there is no strong evidence in the form of multiple discoveries of extra-terrestrial life to support this.

In short we don't know what stars can support life.