Translation:I like art class the most.
It's a better translation. It ought to be an option when using the word bank as well. I ended up writing "I most like art class." which was counted wrong probably because it's a bit awkward in English, but that's because it all seemed wrong. It wanted "I like art class the most."
I feel like "My favourite is art class." should be acceptable. Yes it is awkward as a stand alone sentence in english. I should have probably said my "favourite class", but if the chinese statement arose in a conversation about classes, or was a response to a question about which class is your favourite, the above sentence would be perfectly acceptable. All I mean is there is nothing grammatically wrong in the English translation "My favourite is art class."
I have found that it is best to never use "never" in comments if at all possible. In a language as widely spoken as English I am constantly surprised by how people use English in other countries, and even in one's own country. In a case like this I think "art class" is better than "art lesson" and I am Australian. Saying "I like art lesson the most" just doesn't work for me but could be fine for others.