The Monroe and Dean trails up Camel's Hump make for a quick and relatively gentle climb even in winter. The Long Trail from the North heding south makes for a longer but still relatively moderate trip. The LT hike will bring you onto rocky ledges with slightly more exposure and this may or may not be a challenge you are looking for . . .
For Mansfield, the Hasleton Ski Trail is a possibility, and you can always hike the less desirable and longer route up the road. You can also hike up the LT, heading south. I have hiked up the LT to the Hasleton Trail and down in winter. There is a steep and tricky section on the LT in that section though this past summer I couldn't find it so either they moved the trail or my sense of scary has changed but in any case, this is one section to watch out for.
I have only ever hike Abraham and Ellen via the LT and this I would guess gets icy for the ascent up the Long Trail headed North . . . never done it in winter so I cannot say for sure. The ski trails, if you are allowed to hike them, might be another "easy" way . . . I am sure someone who knows better will chime in . . .
Haven't hiked Killington in winter and will probably just stick to hiking it via the LT going south.
Hope that helps a little.
sli74