Well, it’s better than nothing.
I think Spyware Terminator is better. But as you had problems…
I think there isn’t other antispyware (resident) for free, so Defender will be better than nothing.
If you surf safely, maybe you can even disable it and run, from time to time, better (and much better) AVGas, a-squared, Syware Doctor (Starter Edition), Spyware Terminator, etc. only on-demand.