We cannot compare the two leagues in just a few factors but at least in big competitions like champions league or european league.
With this competition we can determine which club from the league is the strongest.
After all, for me in every league there are top clubs or the best clubs like the Premier League has Manchester city and LaLiga has Barcelona.
So we don't need to compare between the main league and LaLiga because these two leagues have the same strength.
If it is necessary to compare, of course I have to say Manchester city is better than Barcelona if only for the achievements they made last season. Because Manchester city managed to get three trophies last season, while Barcelona only got one, namely in La Liga. So in my opinion the comparison is very striking and even very unbalanced. But on the other hand, I also hope that both of them can do better next season, especially in the Champions League.