Probably Sindarin. Klingon is intentionally linguistically really hard like, no matter what your culture is. There's a big feature with the linguist they hired for star trek 3 on the special features and he tries to use all of the least common word orders, grammar and all that in human language. Sindarin is easier to figure out words that don't already exist as well, it's not made intentionally hard for humans to get naturally. I guess Finnish people have a pretty easy time with Sindarin cause there are a lot of similarities.