I believe Hybrid has allowed modifications and changes that stray from the Classic UO:T2A model. But I don't know this for sure, as I haven't played on that server. It was all hearsay from the guys on Second Age (so probably not even true). I will list Hybrid as a Classic Server as well.
I know that Second Age makes it absolutely as close as possible - including some of the original sucking points, such as having to cut up bandages one-by-one instead of in a stack. To me, that is what makes Classic... even the sucky parts
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EDIT:
I just read Hybrid's intro, and they state up front that they balanced PvP and have increased skill gain speeds - so they aren't trying to emulate classic 100%. They took the T2A era, and made it more casual friendly.