Well, I guess it depends how you measure it the strength of a league & the quality of the football played there. Not sure how to do that objectively, but personally I tend to think that good quality football is played successfully by more teams in Spain than seem to get real credit for it right now.
Do you just look at the quality of the 'elite' teams? Spain's probably ahead of England there.
Number of elite teams? Probably England.
Quality of elite teams just his season? That'd be Germany.
Or do we look at the overall quality of the elite & 'second tier' teams? I'd probably have Spain again, if we're basing it on more than just this year.
I don't really know, but personally I think that if anyone bothers to watch La Liga beyond Real & Barca, most seasons there'll be quite a few good other teams there, with some good players, who play some good football, who get a fraction of the attention of the Big 2. Is it a great league? Absolutely, IMO.