KSRTC operate two daily bus services to Goa from Bangalore. Both are Airavat Club class (Volvo, Luxury type) overnight buses leaving from Kempegowda bus stand (Majestic).

Bangalore to Goa bus timing (KSRTC): The first bus leaves at 7.30PM and reaches Goa 8AM at Panaji.
The second volvo bus leaves at 8.30PM and arrives Panaji by 9AM.

For the return journey the first bus leaves Panaji at 8PM and arrives at Bangalore by 6.30AM. The second leaves at 7PM, and arrives at Bangalore by 8AM.

Bangalore Goa bus route:
KSRTC follows the Bangalore - Yellapur - Ankola - Karwar - Canacona - Margao - Panjim bus route. That is the route is mostly by NH4, NH63 and NH 17, which is a good route from a road condition stand point. Bus leaves from Kempegowda bus stand (Majestic) in Bangalore and there are quite a few pickup points (Yeshwantpur, Jalahalli Cross etc)in the city.

Bangalore Goa bus fare is Rs948. You can book seats online at KSRTC.in

Other Bangalore Goa bus services :

Also private operators like Seabird Tourists, Paulo Travels, VRL Travels, SRS Travels etc operate many overnight AC and Non-AC services to Goa.
Checkout with their websites for schedule and booking. Fare ranges typically Rs600 to Rs1000.

Also there are great range of pickup points at Bangalore for different trips.This also could be a convenience factor for you to select one service over the other.