Certain players couldnt play in certain leagues.

Look at bergkamp. He couldnt cut it in italy yet came here and was awesome.

Technically serie a is the best. Clean sheet is as good as a win out there.
Entertainment or value for moneywise the prem is best. Non stop action unless you watch liverpool or chelsea.
Overall i reckon with a mixture of technical and a bit of entertainment is la liga. Sometimes its quality, altho all sky show is the big four week in week out.