I've some of Toney's fights on DVD (including some of the earlier ones) as well as maybe a quarter of Haglers career. I'll go with Hagler by UD based on workrate/conditioning, ring smarts, mental fortitude and just overall cussed meanness. I think skill, speed and powerwise they're a pretty good match. Marvelous Marvin is simply the greater champion.
This would have been a real battle of attrition. Both had excellent workrate, and no less than great chins. I give Toney edge in handspeed and power. I really don't to pick a winner but if I am forced to, I'd go with Toney.