Depending on the filters you have on your microscope. In my experience ethidium-bromide works quite well. Some authors report that DAPI is not so good because it binds more favorably to minor grooves in DNA rich in AT. However, in my opinion it also as good as ethidium. Other, less carcinogenic dyes are Sybr gold or green which are also good. Again it depends on the filter you have. 

SYBR Green is good but expensive... Ethidium bromide also works good except for precautions to be taken while working with it..

I find that Sybr Gold works the best and can be used at 1/10,000 in dH2O.

Best of luck!

Fluoromount-G, containing 4’,6’-diamidino-2-phenylindole dihydrochloride (DAPI) for nuclear staining is good for nuclear staining