I have to go with "Don't Talk to Strangers" but it is a tough choice. He has many great songs, but I have to say the first two "Dio" releases when Viv Campbell "wanted" to be with him were magical.
Stargazer/Heaven&Hell/I/Caught in the Middle/Shame on the Night/Evil Eyes/RockNRoll Children/I could have been a dreamer.
All time fave: HEAVEN AND HELL
Man on the Silver Mountain
16th Century Greensleeves
Sign of the Southern Cross
Children of the Sea
Rainbow in the Dark
One Night in the City
Last in Line
Egypt (The Chains are On)
Sunset Superman
And All the Fools Sailed Away