Great Britain (not Northern Ireland) uses the d'Hondt system in European elections, with small seat magnitude constituencies (3-10 seats) and no attempt at proportionality on the national level.

Combining the above with ordered party lists where the voters cannot affect the order of candidates on a list, it is about the worst proportional election system which could have been introduced. It is however better than first past the post.

This is the system used in Spain, and the consensus is also that it is a really bad system. First of all, the constituency is the province, electing anywhere between 1 and 34 seats. This leads to overrepresenting small constituencies. Then the D'Hondt system favours large parties, and we have closed party lists.

Currently my preferred voting system is an additional-member system with single-transferable vote. Combining this with open party list for the top-up seats would be the best of all worlds.

Nothing is 'mere'. — Richard P. Feynman