I used to depend on online bus booking portals for my journeys from Bangalore to Kerala, and I mostly booked private service providers for the journeys. After I had a couple of bitter experiences with private service providers [not all are bad, but most of them are stooping to a new low] I shifted to Karnataka KSRTC.
Nowadays the bus comes on time at the Shanthinagar BMTC bus stand and leaves without a lot of delay. There are no last minute changes and hassle, and the staff are professional too. The buses are in good condition (I usually prefer multi axle ones).
And usually they reach in time too. KSRTC, being a Government initiative, truly deserves 4 stars!