Searching diagram illuestrate software

I am a student of Information Technology and now I am in 3rd year. So most of the subjects in this stage are Analysis related and I have to draw some kind of diagram like as class diagram, Use case, DFD, Network security architecture etc. For class diagram and Use case diagram i use StarUML. Last year i used Dia for Network architecture. But it was not so comfortable. Moreover i faced some problems with doing my task. I also want to add that i find five top software name such as Inkscape, Gimp, Scribus, FontForge and Dia. But i need a proper suggestion that which software will be fitted with my works. StarUML is ok but doesn't updates properly.