The expression "plej bona amiko" is long and can feel repetitive. Is there a common or a good way to express the same idea, but in a more concise way?
Slightly tongue-in-cheek: from what I believe the kids these days say, how about pbao/pbaino (similar to, I think, bae in English)? You would probably have to say plej bona amik(in)o during a conversation first, to make sure you're understood.
Otherwise I'd agree with Bjørn's suggestion of amik(in)ego.