For PVP server, the best Client is Interlude.
Maybe the classes are a bit unballanced, but it is the most simple L2 Client, not many items, not many and confusing skills, is just simple and pure Lineage 2. Epilogue have many new items and skills and changes that make the game really complicated for PVP servers.
Now for Retail servers, the best Client is always the last Client that NCsoft creates, that's all.
PS: I think the most people that love IL, think by this way.