Best views are on Race Mountain
The
Mount Greylock State Reservation webpage has a PDF link for Hiking Trail Mileages of all trails in the reservation.
The book
Exploring the Appalachian Trail, Southern New England, by David Emblidge does a good job of covering the side trail mileages for Connecticut, Massachusetts, and Vermont. Near Bear Mt. the Undermountain Trail is 1.9 miles long, Paradise Lane is 2.1 miles long and joins the Undermountain Trail 1.1 miles from CT Route 41, 0.8 miles from the AT. A
loop over Bear Mt. using these trails and the AT is 6.7 miles and 1600' elevation gain. A short walk into Sages Ravine is a short, easy, and worthwhile addition.
Other nearby AT side trails are:
Lion's Head trail to Bunker Hill Road 0.4 miles.
The unmarked Northwest Road from East Street to the AT at Sages Ravine 0.8 miles.
Race Brook Falls trail to MA Route 41 1.5 miles
IMHO the best views on the AT between Salisbury and Egremont are the
cliff views on the section over Race Mountain. If you could spot a car you could combine Bear and Race Mts using the Undermountain and Race Brook Falls trails. The
50 Hikes in Massachusetts book has a 7.7 mile Race and Everett Mts hike from the west (by using the unmarked Northwest Road mentioned above and spotting a car at Mt Everett Reservation). Earlier editions of that book had suggested a shorter loop using the unmarked Plantain Pond road. However, the Plantain Pond road is on a YMCA camp and access is no longer allowed.