Your question Dinesh, I have used both, although I always have Malwarebytes. Malwarebytes is good for a manual scanner, they push out updates a lot, at least once or twice a day.
Spybot is good for Real Time protection, albeit it's maybe overkill. If you have a major AV, and Win Defender with it's Real Time protection, and Windows firewall, and the UAC on, it's pretty much good enough, IMO.
And maybe one or two manual scanners like Malwarebytes to run manual scans every once in a while. If you just wanted to use Spybot for a manual scanner and not having the extra RTP running, you could do that too.
Another nice little program, that sort of acts like the UAC, is WinPatrol. It notifies you when anything wants to add itself to startup. Something that Spybot does too, but it's not as heavy on system resources.